...your entire IMC rating course can be credited if taught by IRI or FI with IR privileges...
There is NO such restriction. See para 6(a) of Appendix 6 to the Aircrew Regulation:
(i) When the applicant has:
(A) completed instrument flight instruction provided by an IRI(A) or an FI(A)
holding the privilege to provide training for the IR; or
(B) prior flight time under IFR as PIC on aeroplanes, under a rating providing
the privileges to fly under IFR and in IMC
these hours may be credited towards the 40 hours above up to maximum of 30hours,
(ii) When the applicant has prior instrument flight time under instruction other than specified in point (a)(i), these hours may be credited towards the required 40 hours up to a maximum of 15 hours.
Thus under 6(a)(ii), up to 15 hours of
instrument flight time under instruction may be credited for IR(R) training. A minimum of 10 hrs of IR instruction has to be completed at an ATO, so if you are good enough and have attained i5 hrs of IFR flight time as PIC holding an IR(R), you will have met the prerequisites. However, you may well find that you need more time to be ready for the IR Skill Test.
The BIR proposal can be viewed in NPA 2016-14. The comment response period ended on 31 Jan 2017 and the CRD is currently being drafted. The final CRD then has to go to the EASA Committee, then to the European Commission and eventually to the EU parliament. Hopefully it will be in law in Q4/2018.
It is intended that there will be an upgrade path from IR(R) to BIR and from BIR to CB IR. Which should meet the needs of most private pilots.