OK, specifically
- The new CBM-IR will not be something I could use in place of the full IR for the purposes of gaining an fATPL/ATPL
The CBM IR will be equivalent to any other IR for the purpose of a modular ATPL course.
- The IMC rating does not currently count towards the CPL or the full IR, nor will it do so even if the new EASA proposals are implemented
The CBM IR is a "full IR". It is a method of attaining that IR, not a rating in itself.
- The training and TK requirements of the full IR will be completely unchanged if the proposals are implemented
The CBM IR is a "full IR". The existing route to the IR may still exist alongside it.
- The UK IMC rating will count towards a CBM-IR, but not towards the EIR, so if I did the UK IMC rating and wanted to fly the airways in europe as a PPL I would either have to do the CBM-IR or start all over again and do the 15 hour EIR
You can get 5 hours credit for previous instrument flying towards the EIR. I wouldn't bother. Upgrade to the full IR. Both require a minimum 10 hours in an ATO.
- The hours from a CBM-IR will not count towards a full EASA IR if I decide to switch from private flying to commercial flying
The CBM IR is a "full IR". It is not restricted to private flying.
If what you get in the end is the same, with the same flight test, why then is it not possible to attach to a full ATPL (referring to Level Attitude's post), or even have it credited to the typical IR (I'm assuming that conclusion is correct)?
Because LevelAttitude's assertion that "the proposed CBM-IR will only be able to be attached to a PPL or a CPL" is incorrect. Read the CRD.