You do not need 'approved' avionics in a kit plane to have IFR capability.
Sure, as a sub-ICAO concept.
Sub-ICAO, you could strap a pair of wings to the top of a Zanussi (not Miele; too good quality) washing machine and have it IFR approved
(I will resist saying that rather a lot of them have been sold
)
no heavy unreliable vacuum system reqiured.
One can have that in the "proper" stuff too but it can be a bit involved. With two alternators (one of which can be just a little one) you can certainly go all-electric nowadays. I am looking at doing that, one day, but the paperwork is too much right now.