Well you can use one for business (ignoring the hobby point) if you have full known icing protection and still accept a small number of flights may have to be cancelled. That is what I am doing now.
But are you doing "formal customer visits"? If so, your customers are, I would suggest, a little unusual to accept you not turning up.
Every other sort of "business flying" is easy.
and can fly at FL250
You have a PA46 
To my earlier post, I would also add that much depends on where one is based. If based at Bournemouth, Southend, Biggin, Cardiff, etc then you can fly day visits into Europe (be back same day) even in today's kind of wx
EGKA 071420Z 22008KT 9000 BKN008 08/06 Q1026
EGKK 071420Z 20006KT 170V230 9999 BKN004 07/06 Q1026
EGKB 071420Z 23007KT 9999 -DZ BKN005 07/06 Q1026
A few years ago, one high profile UK pilot did a documented 49/50 despatch rate, over a 12m period, business flights and customer visits. But he did it in a Cessna 421C, and was based at Bournemouth, and he was flying to major European airports, so he had the whole lot. In Europe, most of the bigger airports (that have Customs) have an ILS. I think his despatch rate would have been the same in a PA46 because that has a radar also. If I recall right, his 1 cancellation out of the 50 was a turn-back to the airport of departure because his radar showed a solid wall of CBs, so that would have been an "interesting" flight without radar.
if I had to fly down at FL120 there would be some flights I have done so far that I would have cancelled due to not wanting to sit in an icing layer for hours
If I had a FL120 ceiling I would not bother getting an IR, because Eurocontrol routes start to get good at FL120+ and I would be flying in IMC much of the time.
I know many pilots (not carrying oxygen) disagree with that but it's confirmed to me well enough on so many flights.
It's just typically European-regulation-perverse that one needs oxygen to get decent IFR routes
I think unfortunately the cost of known-icing fitouts means that only higher end GA singles get fitted with it and I assume almost nothing in the rental fleet would have it.
That's probably true, though I know of some (clapped out) stuff like an Aztec which can be hired.
But what is the meaning of "known icing"?
That is a rather US-centric term. If it is to be enforced, then in terms of deciding whether a given flight was legal, one needs to define the pre-flight decisionmaking process and how it maps onto specific weather services.
In the USA, this has varied and at one stage the FAA ruled that any flight in potentially icing conditions (IMC below 0C) was "known ice". The resulting uproar resulted in that being removed and now it is much more down to the pilot.
Frankly I don't know what it would take to get criminally charged, upon a landing from an incident-free flight, for a departure into "known ice" in a non-FIKI plane, FAA Part 91. Or for that matter in an EASA-reg.
European weather services are rubbish compared to US ones, and e.g. the UK Form 215 (which I consider to be almost unusable because the forecaster throws in everything including the kitchen sink) forecasts icing in all cloud regardless of temperature
Are there any passive methods of reducing ice accumulation, eg surface treatments / materials (even if not certified) that ice doesn't like sticking to?
AQ
Broadly no.
The thing about that paint is that you could apply it to your plane and it would be 100% legal to do so - because it's "cosmetic".
(I am assuming it doesn't affect the macroscopic airflow).
It won't get you FIKI certification, but what is FIKI certification anyway, in the private flying (non AOC) context?
If you launch into "obvious" icing conditions in a non ice certified plane, that is just negligence (at worst), and insurance covers negligence, so insurance will still be valid.
If/when that stuff comes in a can, and assuming it is reasonably robust, it will be a revolution.
Yes. Neverwet
It is not on the market yet.
So that is more like a no then?
Is this any more than a better RainX?
There is stuff which unofficially, reportedly, allegedly, Swiss Air Force pilots paint on their leading edges, from here.
It's supposed to work for "long enough"
I have a free sample bottle of it, labelled "BVBA/SPRL", on the shelf but never tried it.
Remind me not to fly through chocolate sauce! :) Neverwet does look interesting...and along with RainX on the windscreen could buy time for climbing through icing....although not FIKI (an FAA concept as you say Peter)...
I also saw [this]
on Avweb...so it is not beyond the realms of possibility that technology will allow currently non de-iced light aircraft to be safer in icing condition in the future....
AQ
I think FIKI may be an FAA term but to me it means and aircraft that is equipped to handle light to moderate icing well. It means wing and tailplane anti-icing and de-icing, prop anti-icing and de-icing and windshield anti-icing and de-icing.
Of course it doesn't mean all icing is irrelevant but ultimately it is a statement that the aircraft systems are made to deal with it in the key affected areas.
Don't put rain-x on plastic windows.
I have read of pilots who did it and their windows went dark.
Rain-X is for glass only.
