Chickenhouse you nailed it there..
I have a SU-29 grounded because of this.
EASA has made it possible to register such planes under a C of A.
The amount of paperwork needed is so huge, and the maintenance facilities (Can't publish names here) EASA approved both paperwork and maintenance so bad, that in the end you don't get what you pay for, if you are lucky to get your plane back without cosmetic damage done during careless maintenance.
These aircraft are almost exclusively operated by private owners. They are not used for training, They have stall speeds and wing loadings often incompatible with General Aviation certification requirements. Spares are difficult if impossible to find (Sukhoi's) other than engine parts. There an an insignificant number of them around, and there is no company or factory back up to issue SB,s, mod's, improvements.
The paranoia of EASA for regulations it's that they will provide for certification under CofA for aircrafts which, because of the issues above, belong Experimental category, so to make them fit into the "Certified category", they embark into endless amendments, and produce so much waivers, that it ends up as a joke, a sad and expensive joke for owners...
Another example how bureaucracy has lost touch with realities, leading to a dead end. This is what happens when regulations are drafted by lawyers in the light of potential litigation prevention and not by qualified people.