> They will get the huge benefit of unquestioned access to CAS which was previously denied to them for no reason other than (often unpublished) policies of the various ATC units
In UK yes, but In Belgium and Germany for example you have no problem to fly VFR in CAS.
There were several issues on that occassion:
Of course ATC will eventually help you by reading it out, but that isn’t a very professional solution. It makes GA appear in bad light to everybody else on the frequency. The degree to which this matters is a matter of opinion in the GA community but you can tell what my view is 
Not my experience – I actually got a Le Bourget SID assigned by name. And could not find it
I must admit this has happened to me too on one or two occasions. I told the TWR controller but he just replied I would get vectors anyway. And in any event you will need vectors to join one of the segments of the departure, and before that you would need to fly the multi-directional departure. I think that this business about joining a departure procedure of another airport named in the clearance is just plain nonsense. It is however good to study those departures because they will give you a sense of what route you can expect to get to your first en-route segment.
Of course, in practice, if the pilot knows how to fly approaches (which he/she must, otherwise any flight in IMC is IMHO eventual suicide) and knows the terminology (same comment) then if he files an “I” flight plan and flies it end to end, nobody will know unless the ramp checker is very well briefed.
But I suppose you could say that about any illegality
“Any reference for not being allowed to fly STARs with an EIR?”
“I am not sure where the current reference is. It was clearly in the original EASA proposal …”
Found it – AMC/GM page 92:
AMC1 FCL.825(a) En Route instrument rating (EIR)
GENERAL
Since the privileges of the EIR are only to be exercised in the en route phase of flight, holders of an EIR should:
(a) at no time accept an IFR clearance to fly a departure, arrival or approach procedure;
(b) notify the ATS if unable to complete a flight within the limitations of their rating.
I note that the reference for this is GM1 FCL.825 (not AMC1 …) in the common response document (comment #589). For some reason, in the final document it has been moved from Guidance Material to Accepted Means of Compliance. Makes it more of a no-no for the pilot.
You will always get a multi-directional departure from Pontoise followed by radar vectoring
Not my experience – I actually got a Le Bourget SID assigned by name. And could not find it 
But now Pontoise has no Customs so I am unlikely to ever fly there again. I would fly to a non-Customs airfield (i.e. with a landing on the way) only if it was really worth it.
Anyway, what this illustrates is that you need to be ready and prepared because you can never be quite sure of the procedure.
A SID is always assigned at a CAS airport. It may not be a published one. It may be one published for another nearby airport (a popular habit at the Paris airports). Or it may be a “multi directional departure” which is a SID made up by ATC.
A SID is not always assigned at a CAS airport. A multi-directional departure is not a SID.
And yes, from Pontoise your departure route will most often follow a SID from Le Bourget because that is the way to separate you from traffic to/from De Gaulle. Pontoise has no SIDs. Pontoise is in CAS ( class D). You will always get a multi-directional departure from Pontoise followed by radar vectoring, followed by a direct to some waypoint once you are no longer a factor.
Any reference for not being allowed to fly STARs with an EIR?
I am not sure where the current reference is. It was clearly in the original EASA proposal and was well known and discussed at the time. I was one of those who sent in a dissenting view, basically saying it will confuse the hell out of ATC, and the SID/STAR procedures often join the enroute section too far from the airport and there is no real way for the pilot to obtain/forecast the wx conditions at that spot and at that altitude to see if they will be VFR (i.e. suitable for legally cancelling IFR). EASA printed this view in their collection of “stakeholder” (such a fashionable word) comments but threw it out.
even VFR pilots are allowed to fly an ILS – under VMC/VFR
Of course, but an EIR holder won’t be allowed to do the same. He will have to formally cancel IFR first.
So SIDs and STARs are definitely assigned to light a/c in Europe, and those mentioned are definitely not a beeline.
A SID is always assigned at a CAS airport. It may not be a published one. It may be one published for another nearby airport (a popular habit at the Paris airports). Or it may be a “multi directional departure” which is a SID made up by ATC.
A STAR is very often assigned in the radio calls (even for busy airports like Gatwick EGKK or Heathrow EGLL) but is rarely flown whole, because you get vectors. The cases where it is flown whole might be where ATC has no radar. I have had this in Italy (LIEE) and Greece (LGAV).
the EIR is a political product, with very little operational foundation for SEP pilots
I remain puzzled by the EIR. It will be very good for “clever” touring pilots who currently fly “VFR” and know how to play the game to deal with the odd, ahem, cloudbreak. They could not officially fly an IAP before and they will not be able to fly an IAP with the EIR. They will get the huge benefit of unquestioned access to CAS which was previously denied to them for no reason other than (often unpublished) policies of the various ATC units. But it will require a more “clever” pilot than straight end to end IFR which is really pretty straightforward once you know the general protocol of how to play the weather versus aircraft performance and how to play with ATC.
“Paris” can range from very quiet (e.g. Pontoise) to very busy (Orly, CDG, I guess) but the latter are way too pricey for light GA and anyway being Class A will be no good for an EIR pilot. Same in the UK, with all busy airports being in the 500-600 quid range so you won’t go there unless you are on fire.
I now consistently get the TRO7T, PEXIR7T or VELOL7T arrival to LFPT although I have never flown the whole procedure. I eventually end up being vectored or getting DCT PON. I once got the ABB1Z departure from LFAT. The only time I went to EGJJ I got the BENIX5A departure. So SIDs and STARs are definitely assigned to light a/c in Europe, and those mentioned are definitely not a beeline.
I can to a certain degree understand that EIR does not give access to flying SID and STAR. Those can get really intense in busy airspace like the Paris are where you can get multiple altitude, heading and frequency changes in quick succession. That said the Paris airspace is class A, there are other airports where they are a breeze, and the workload would not necessarily be any different if vectored.
Will the change of rules (VFR-IFR-VFR) confuse ATC? Take up time on the frequency?
Definitely. One wouldn’t normally depart an IFR airport with a Z plan.
ATC will not necessarily know if a pilot is EIR or IR rated
ATC will definitely not know it.
Again, the EIR is a political product, with very little operational foundation for SEP pilots.
