Sorry if some of these IRs are confusing ; ) if we are talking about the enroute IR where you have to drop out of CAS before the STAR and cannot fly an instrument approach then there are a number of safety issues
First, I don't think you have to "drop out of CAS". I don't see an inherent restriction or rule that prevents you from cancelling IFR while still inside CAS - unless that CAS happens to be class A. The only real issue is that you have to (be able to) descend into VMC and cancel IFR, before dropping below the MSA/MVA (or whatever it's called). Whether that happens inside or outside CAS is largely irrelevant as far as I can see.
As far as the rest is concerned, yes, I see and share the concern but shouldn't that be solved by normal planning: Making sure the flight can be executed within the privileges of your licence?
You should not commence a VFR-only flight if the forecasted weather is below VMC anywhere on your route, or have a solid plan B.
You should not commence a Y or Z flight if the VFR portion of your flight is below VMC anywhere on that part of your route, or have a solid plan B.
You should not commence an IFR flight if your origin or destination is below IFR minima, or have a solid plan B (which, admittedly, is easier to create and execute than the previous examples).
And with the EIR, the additional consideration is:
You should not commence an EIR flight (a VFR-IFR-VFR flight executed with EIR privileges) if your origin or destination is below VMC, or have a solid plan B.
In all cases you've got to keep up to date with the en-route and destination weather during the flight, to avoid being suckered into a situation where there is no easy or legal way out.
And as for trouble en-route: The exact same would be true for VFR-on-top flights, or for instance SEP flights over water: It becomes a risk management issue. In those cases, I'd prefer doing an EIR flight (high, in the airways, with constant ATC oversight), than doing the equivalent flight as a VFR or VFR-on-top flight. After all, in large parts of Europe, VFR or VFR-on-top means at a significantly lower altitude and with less ATC support compared to an IFR flight. Up high it's all class A (or class C with additional restrictions that for all practical purposes it's class A anyway) so if you want to have safety in altitude, you need an IR or EIR.
I can well imagine that from the point of view of a full-IR rated pilot, the EIR seems to be a step down in a lot of things. But from the point of view of a VFR-only pilot it's a very welcome step up. A step up that can bring additional safety, as long as you use it responsibly.