The US requires certified avionics for IFR for obvious reasons: uncertified avionics are ok for enroute but have no approach capability. The databases are owned by Jeppesen and Jepp don’t license the data to non-TSO box makers.
If this has changed, it would be very recent.
In the meantime, in Europe one can pretend all kinds of stuff but it will never add up.
Peter wrote:
uncertified avionics are ok for enroute but have no approach capability
According to EEA this is not correct in general. I don’t know what the specs are, but according to the EAA a certified GPS navigator is the only way to go. Now, this could certainly be a pure practical/economical consideration (as said previously), but why install IFR aviation equipment that has little or no practical value?
For US airspace, I don’t know the avionics requirements for IFR enroute.
But regardless, enroute capability is immaterial if one cannot land under IFR and for that you need to fly
or some combination of the above, according to your risk preference and where you fly geographically.
They do indeed, plus you can base an N-reg EXP in Germany for 180 days and then just keep re-applying (other threads) for ever, but there is the small problem that you can’t fly IFR anywhere out of Germany AFAIK (except possibly to some specific places to the east – would need to review the other threads) 
It is no coincidence that if you watch the 1-2 actually flying Lancair Evolutions on FR24/FA (visibility is inevitable if you fly IFR) they are all flying in certain places 
I would still equip a plane for “full IFR” (especially ILS) even if it was EXP – simply because clouds are everywhere, and 100% legal VFR is basically impossible (except in Arizona, etc).
Peter wrote:
They do indeed, plus you can base an N-reg EXP in Germany for 180 days and then just keep re-applying (other threads) for ever, but there is the small problem that you can’t fly IFR anywhere out of Germany AFAIK
The beauty of the Brussels or rather Cologne bureaucracy is that once someone somewhere accepts something, this “OK” is usually valid across the continent. Look at the financial services industry, same rules apply.
Coming back to the subject, many (most?) countries accept limitations in permit to fly as issued by the host county. No questions asked.
RV14 wrote:
The beauty of the Brussels or rather Cologne bureaucracy is that once someone somewhere accepts something, this “OK” is usually valid across the continent. Look at the financial services industry, same rules apply.
That’s true, but only for matters which are regulated at the EU level. Experimental aircraft are expressly not regulated at the EU level but at the national level.
many (most?) countries accept limitations in permit to fly as issued by the host county
They don’t.
Peter wrote:
many (most?) countries accept limitations in permit to fly as issued by the host county
They don’t, but that’s another topic
Someone would need to go trough the AIPs and compose a list
It’s been a while since I checked
Airborne_Again wrote:
Experimental aircraft are expressly not regulated at the EU level but at the national level.
true, but EU CAAs trust each other
RV14 wrote:
true, but EU CAAs trust each other
This is not a question of trust (i.e. whether a particular homebuilt aircraft is suitable for IFR) but of policy – or culture (i.e. whether they allow homebuilts to fly IFR at all).
Recall how the German CAA tried to sabotage IFR in class G (and to some extent still do), even though in many countries there has always been even airline traffic in class G.
