I dont fully grasp your aversion to joining at our near the IAF.
There are a number of reasons.
1. As you point out, it's not going to work for many IFR airports from ATC's point of view.
2. Obviously it's not going to work at VFR airports
3. Let's imagine an airport with IAFs and with no problem for ATC. Well, in this case, as a pilot, why do I want to be overhead at 3000' when I can plan a VFR arrival that allows me to be on the ground at the IAF? If the IAF isn't at the overhead, then it's likely to be miles and miles away from the routing of a sensible VFR arrival.
I am not saying there's never going to be a scenario of the IAF being the transition point to VFR. I just doubt it will be systematically so, and that in practice what could happen is pretty much as it is today for VFR arrivals to IFR airports (note: VFR arrivals, and not IFR arrivals accepting visual approaches) where I think IAP arrivals are less common (perhaps Soton is an exception).
making up your own descent perhaps many miles away from the airport while leaving the protection of CAS and having less assurance of the actual cloudbase where you expect to pop through
I am afraid this is the essence of the EIR. A pilot who doesn't like it will need a full IR or to stick to VFR. But let's not escalate the enroute descent into something scary and abnormal. It's what private IFR pilots already do when they operate to VFR airports. This is not a special case. It is the norm, day-in day-out for many IR and IMCr holders.
brgds
421C