to be fair (and to avoid spreading disinformation) none of the new ideas were possible to be implemented years ago. for instance, if BGFX was available 5 years ago we would have added cross platform shaders long before. but the alternative was to hack around a lot of windows-only code with no core support, and that was not really interesting. similarly, LUA has been present in MAME for almost two years and nobody ever suggested to use it for adding back hiscores... I'm pretty sure there would have been zero resistance, but simply nobody was interested enough
also you are sort of ignoring the fact that a lot of new features were added in the past two years. maybe less impressive and groundbreaking than the more recent ones, and definitely less advertised, but to my knowledge they have been highly appreciated in some niche communities. Just to mention a bunch of stuff we added - MAME/MESS added support serial connections (RS232), allowing exchanges of file between emulated machines and home machines - MAME/MESS added support for midi input/output, allowing for instance emulation of The Miracle Piano through a real piano keyboard and some progress in synth emulation
there had been also tentatives to renew the internal UI, and they were not rejected based on being "a change" but due to bugs (which was a shame because I actually liked Nathan's UI proposal)
in conclusion, these are very exciting times for MAME but it's not like we have been sitting in idle for ages as you seem to suggest