I think it's a non-issue because when the weather is such that somebody might want to use an IAP to get into a place like Stapleford or Wellesbourne, the place would be like a graveyard.
Today was a super flying day, and I was up for a few hours, but with 20-30kt surface winds it was very quiet indeed. Anytime vis is below say 7k, I am happy as a pig in s**t but there is hardly anybody about.
So you would never actually have a "Stapleford" with six in the circuit (plus another three doing "real man circuits" i.e. inside the other six, cutting them up as they feel free) PLUS somebody doing an instrument approach, under conditions where there would be a separation problem between IFR traffic and VFR traffic - because the IFR traffic would be in VMC and would have to look out.
Actually Stapleford and Wellesbourne and probably poor examples; with Welshpool and others they have an on-site navaid and without a doubt have unofficial instrument approaches already, CAA-authorised for certain based operators. So............ how do THOSE work, on a field with no ATC? I reckon they work exactly as I describe; they get used only when the place is like a graveyard.