The EAA has a document that strongly suggests that IFR operation in Experimental Aircraft is legal. The necessary equipment is described in 91.205. Provided all this is met, as well as all other IFR requirements (e.g., pitot check, appropriate engine, etc.), I think instrument rated pilots are ok to fly IFR in an experimental.
However, in a question related to a checkride in an LSA, Can I do an IFR checkride in an airplane that isn't certified for IMC? , I learned about another concerning aspect. It says:
the Instrument Practical Test Standards (FAA-S-8081-4E PTS Instrument): Aircraft and Equipment Required for the Practical Test The instrument rating applicant is required by 14 CFR part 61 to provide an airworthy, certificated aircraft for use during the practical test.
[my boldface]. Putting all this together suggests that I can train and fly in true IMC in IFR in an experimental aircraft, but I cannot take my checkride in one. Is this interpretation incorrect? Are there (m)any cases in which checkrides were done in experimentals?
PS: I sometimes wonder whether we are training to become pilots or lawyers...