And an avionics fit which is truly useful for IFR (VOR, ADF?, DME, LOC/GS, IFR GPS, autopilot!!) is simply not going to feature in most homebuilts, due to cost and weight.
It is bizzare that clapped out 1970s iron can be IFR approved, but there we are... they got in by the back door, in the goode olde days, but this argument cannot be used to let other types in.
Please, do explain what exactly is the problem with flying IFR in a bit of "1970's iron" (say, a PA-28) that has dual VOR, ADF, DME, LOC/GS, GPS and a KAP-100?
I'm a low hour PPL with a view to getting an IR at some point and of course the flying club I'm in has a bunch of ancient PA-28s from the 70's and 80's that are all flying along very happily, despite their age. Compared to a modern SEP like a Cirrus or Diamond, what, in your view, makes these old aircraft unsuitable for IFR ops?