I really like how diverse French India is, both in terms of population and of thought.
But just for clarification... does the départmentalisation plan mean for Yanoan to be on its own, while both Karikal and Mahé to fall under the Pondichéry départment?
Yanaon will be its own département, Karikal and Pondichéry will be one département, and Mahé ... is mostly seen as an embarassment by départementalistes. The common plan of the Socialistes is to offer Mahé a referendum and let it ask to be attached to the British Raj, as there is no French resident in the city apart from the bare minimum (a representative froom Pondichéry and a Greffier de Justice).
The reason for Karikal and Pondichéry to be seen as a future united département is that they are close enough and are expected to work like most French overseas work in this world (one département split in a small number of highly competent municipalities). Yanaon on the other hand is really further North, and is Telugu, while the other cities are mostly Tamil.
EDIT : Woops, I just noticed the mistyping. I meant only one département for Pondichéry and Karikal (Fixed it)