Let me float a whimsical(?) idea about Samuel Beckett's adoption of French over English as the language for so much of his writing. You have a man who "rejects" Ireland in so many ways and for so many reasons (especially as it is dominated by the English government and the Roman Catholic church from beyond its shores); is it not almost natural for him to further distance himself (aesthetically and politically) by rejecting the language as well as the society and government? Too whimsical or frivolous to be sensible you say? Well, it is just a long pondered thought from someone who has studied and has been fascinated with Beckett for more than forty years.
Beckett's case is further complicated by the fact that he was born a Protestant. It is interesting that Joyce, who detested the Irish church (if only for its treatment of Parnell) had something of soft spot for the French church. I think your thesis is pretty sound, actually.