I dont understand your point. The PPL is not limited because it was always constructed to be ICAO. The IMCr couldn't be ICAO. An ICAO member state is obliged to accept ICAO privileges, but because an IMCr is not ICAO you cant oblige another ICAO signatory to accept it, but you can leave them to make their own decision.
My point is that the ANO says as a PPL you are restricted to flight in VMC conditions only. These restrictions apply worldwide, as the ANO applies to you wherever in the world you are flying when using a UK licence. It then goes on to say that with an IMCr within the UK some of those restrictions do not apply (ie you can fly in cloud).
To summarise:
Worldwide: normal PPL privileges with VFR only
UK: IMCr privileges, within UK only
= VFR only outside of UK.
So I'm puzzled how you can then say that the IMCr is valid outside of the UK based on the ANO. I know what you mean about CAP804 saying otherwise, but the ANO overrides CAP804.
A clever lawyer could probably argue otherwise in the unlikely event of the CAA prosecuting. But the CAA do have the legal right to revoke a licence without going to court. So if they say you can't fly on an IMCr in France, then I for one would not want to risk losing my licence for that.
If DGAC intend on the IMCr being fully accepted in France then they should do what the IoM and CI do - include it in their ANO or publish an exemption as the CI do for the NPPL. By doing neither, it doesn't look like it is official DGAC policy or their intention for it to be. More likely an administrative error by somebody who isn't sure what the IMCr is.