I'm glad someone else thinks along the same lines. I've felt for quite some time that Class E control zones would be the best 'compromise' for want of a better word. It allows ATC to work with the full IFR picture without restricting VFR flight whether GA or otherwise. I'm surprised there isn't more support for it in the UK really.
I don't think class E would make a significant difference to the risk, and it would significantly increase the complexity of the airspace.
Your class E would protect against flights in IMC crossing an approach at relatively low level. Since the traffic density in IMC at low level is very much lower than in VMC at low level, the risk of collision is small to start with. To the best of my knowledge, there have been no collisions in IMC in the UK for 30 years, probably much longer. Of those potential collisions with IFR flights, most of the transiting IFR flights would be talking to local ATC, whether there's class E there or not. Thus the class E would be very unlikely to be effective in actually reducing the probability of a collision.
The much greater comparative risk is a collision with a VFR flight crossing the approach track in VMC. The traffic density is much higher, and the high workload of an approach means that the ability to see-and-avoid a random VFR flight, which in a fast aircraft is very limited at the best of times, is low. And VFR flights are less likely to be in contact with ATC. But your class E does not prevent a VFR flight from flying right through the localiser at 3 miles.
If you need controlled airspace, you need at least class D airspace.