In Norway we have 10 finished and registered (some regrettably have crashed). Altogether there are 46 experimental aircraft registered. This make 22% of all experimentals RVs In the ultralight category (max 450 kg) there is a whole bunch more though, much more than experimental registered.
24 RVs are currently in vareous states of the building process (out of 63). The percetage of RVs under construction is 38.
Hmm, this should mean that you are much more likely to finish if you are NOT building an RV