For the time being, this national rating is valid in French airspace only, but Peter's right, it could morph into something pan-European.
The following comments were published by AOPA France:
This is a French only rating.
How can it evolve in the future?
AOPA France and the French CAA have been very careful to stick to ICAO requirements and exceed them in all aspects of the training. Therefore, the French Instrument rating for Private Pilots is ICAO compliant.
EASA, the European Aviation Safety Agency, has put together a working group that is working on solving exactly the same problems that have given birth to the French rating. We are hoping that the French experience will be used by EASA to speed up the work undertaken by the FCL 008 workgroup.
In the meantime, other countries in Europe could decide to accept the French rating as an ICAO compliant rating, signing a sort of bilateral agreement with France under which French rated pilots could fly into other European countries such as Germany, the UK or any other European country.
If enough European countries accept the French rating, EASA could decide to adopt a system that is already functional and has been proven as a functioning alternative.
The first candidates should be taking their exams (written and practical skill test) as early as September.
The full text, with further background info about the content of the written exams is
here (scroll down for English)