I hate being coaxed to unlurk.
I think that there is some confusion here which needs to be addressed.
The Boeing 777 was an experimental. This allowed the development to occur with only engineering considerations at play. when these had honed down the best solution to a dilema the verification paperwork could then be commenced toward the final certification. this achieved economies by allowing paperwork only on the final design solutions.
Experimental Amateurbuilts are a whole 'nuther field. The basic tennet is that it is your personal right to build an aircraft and to test fly it, then go on to use it for enjoyment.
The amateur test flying will usually only lead to one aircraft beng involved and personal knowlege gain.
In dununda the ABAA streamlined certification for amateurbuilts saw almost no new designs. Of the hundred or so designs that have an ABAA (amateur built aircraft approval) most were american "experimental" designs accepted on the basis of safe history. dununda finally moved to experimental because the ABAA system was dead.
I think mixing the test flying considerations for commercial experimentals and for amateur experimentals is flawed. They have different purposes and outcomes as regards the number of produced aircraft and thus the public risk is different.
I have no problems with either occurring.
I have modified the homebuilt I fly, improved it and test flown the mods.