I don't know the answer to the conversion (if indeed this is in any way finalised) but how much dual training you will need to pass the IRT will depend on the syllabus and the actual training setup.
I have just done the FAA IR to JAA IR conversion and took 20-30hrs (depending how you count it - I had a break for some weeks, which is a big currency killer for that particular type of hand flying NDBs etc) and it is readily apparent that the biggest factor by far is whether NDB procedures remain potentially in the IRT (which I am sure they will) and if so what the tolerances are.
Some 80% of my 20+hrs were spent on NDBs.
For example, the requirement, on the NDB hold, to be established within 5 degrees on the inbound to the beacon was reduced from 30 secs to 15 secs and very recently to 5 secs. However, on an NDB approach, you cannot descend from the platform until you are within 5 degrees of the inbound track - end of story! And if you ever go outside that 5 degrees limit, you have to go around. In reality, the NDB system is so crap that examiners cannot work it rigidly, but how good do you need to be? It's a matter of judgement, for whoever is training you and deciding whether you need to do "one more flight" before you are good enough to be given the 170A course completion certificate and to go for the IRT.
That's before one gets onto the 170A "pre-test test" stuff which some FTOs run as a bit of a scam to make more £££, on which there are no defined standards, and the 170A examiner might well choose to operate the 30-second requirement.
I believe the CBM IR will allow a defined credit from previous instrument time, up to 40hrs. But IMHO you will still need to allow for say 20hrs FTO time to reach the IRT standard. But maybe not - nothing stops you being a bl00dy good pilot via unlogged flying; the difference is that now you will need just 10 official dual hours whereas previously it was 50, which is a big cost difference for people with "inadmissible" training/experience.