Should crypto projects build BTC reserve funds, or should they focus all their resources on developing their own ecosystems and solutions?
Why not? They are all shit coins after all. Probably the developers know that already and trying something different that can help.
Will ADA & DOT prices be supported if they have BTC reserve funds?
I do not think there is any problem except the project is becoming a dead project. USDT company bought bitcoin and went into bitcoin mining and still USDT is leading in stable coins.
Are you planning to buy ADA and DOT? Or will you sell them from your account?
If their prices fall significantly, I can give it a try and gamble with both.