Presumably, the risk of FAA IR holders waiting till EASA is done, in the hope of doing just the 4 exams (AIUI) carries the risk that the EASA FCL proposal will suffer a substantial meltdown.
Then there might be 2 outcomes:
1) A reversion to the present JAA IR conversion regime (15hrs flying, if which about 10 can be in a sim) plus the 7 exams
2) A loss of all conversion options for private IRs (not wholly without precedent; back in ~ 2001/02 there was no PPL/IR route at all and one had to sit all 14 ATPL exams, followed by a "reduced" CPL/IR checkride).
I suspect it is #2 which may be worrying some people. I wonder how likely it is.