The only thing I know to ask is,
1. "Gom asoni"
2. "Bathroom Koday?" and
3. "Oba - Doizza koddur?"
There is quite a sprinkling of Arakanese words in the Chittagonian language.
This is a bit off topic but what the heck - I'll bite just for once. Without starting a flame war, we can say that in the system of languages, the hierarchy of languages is distributed thus (according to Wiki which is derived from Banglapedia),
Indo-European
Now you might disagree - but this is what was agreed to by Sylheti language scholars as well as 'experts' in the linguistic field after they studied the language. We can all have our opinions but linguistics is its own field with fairly well established norms and rules. I don't want to delve into that subject right now. If in doubt - google it.
I don't know what can be proven by the inference that Sylheti was derived from Hindi rather than Bangla, but the linguistic proof we have belies this inference. In fact Sylheti has a fairly large number of Assamese borrowed words in it. One could almost call it a polyglot (mixture) of Assamese and Bangla.
Sylhetis in Bangladesh are already in the most privileged positions. I have members of my extended family who happen to be Sylheti and they are all upper class people. Other than the need of talking to other Sylhetis - they are happy speaking Bangla. Bangladesh is already such a small place, what's the point of driving more wedges into its linguistics structure?
BTW -I make it a point to learn regional languages every chance I get. They're great ice-breakers at parties and get togethers...