I would respectfully disagree with the view that BAF either
a) cannot afford or
b) does not want
air-superiority or at least air-defense assets.
To wit,
1. The dispersed airfields during PAF times are still available and some have been modernized in the last five or so years.
2. Because our AF budget is on the low side, there won't be a priority to equip BAF well at this time.
However I would posit that the BAF (along with all other armed national defense services in Bangladesh except maybe Home Ministry/RAB or armed police) do possess independent decision-making ability on their asset budgeting and procurement. Hasina plays it nice with the armed forces and leaves them alone. Doing otherwise has boded ill for the tenure of all PM's historically.
All Chief of Staff of the armed forces maintain tactful protocol with the Prime Minister and it is reportedly a quid-pro-quo situation.
They run things independently without undue influence in civilian affairs. And in return they expect and get the arms that they feel they want per the overtly published 'Forces Goal 2030' and other covert assets. Building the Navy is the priority at this time for obvious reasons. BAF is the third child after the army and will get leftover funds for now.
While Bangladesh won't be getting 4th Gen. air-superiority fighters anytime soon (your assessment is accurate about overt neglect of BAF), we still can't rule this out being available in small numbers for training needs. We won't be trumpeting the acquisition of assets and asking everyone in the neighborhood for their opinion on this, It happens when it does. I trust the judgment of the senior BAF leaders. They understand that their country is not on a war footing and that funds are limited for expensive defense purchases.
That said - for a country in Bangladesh' defense posture profile, we have had both the Navy and Army's air wing equipment heavily modernized. SHORAD defenses have also been deployed along the coastline and at logistics points.
While you are accurate about not ignoring the whims of Modi administration in this PM's tenure, things could be different in the next one. No administration lasts forever. And no administration in Bangladesh being a smaller neighbor within SAARC (which we mooted by the way) can ignore subcontinental Geo-politics.
I will finally say that signing a 'defense treaty' with India is rather out of the question. My prediction is that Bangladesh will rather choose to turn into Afghanistan if that is even attempted and that is not what policymakers in Lodhi Road even want. No one is trying to turn Bangladesh into 'Ram Rajya' and the price will be too steep.
I'd also say (a little OT) - that India's concern is a 'stable economic market entity' for selling a combination of the likes of 'Amla Hair oil' (FMCG goods) and textile looms (capital goods) and they are happy with that. If Pakistan wants to sell us FMCG, Capital goods as well as do business, we are open for that too. I personally know quite a few Pakistani families who do active trade in Bangladesh in the textile sector.
Overall a good post but I would not be surprised if BD was to have 4 squadrons of 4+ generation fighters in service in time for it's 50th birthday of independence by 2021.
We need to remember that BD economy is currently US 220 billion dollars and growing at 7% a year. The growth rate is likely to pick up to 8-9% over the next 2-3 years as projects like Padma bridge and the 4-laning of major highways is completed one after another.
Sparing 2-3 billion dollars for purchase of fighter aircraft by BAF should be achievable in the next 5 years.