Many of the recent drops in crypto currency (both BTC and other alts) have been due to threats of government sanctions & regulations.

They all went down because of that threat, not just because of BTC going down.

Furthermore there are several exchanges that allow more than juat BTC to be traded for fiat. (CoinBase, for example allows Direct purchase of: BTC, BCH, ETH, and LTC).

Lastly, there have been alt coins that don’t move in the same direction as BTC. Sometimes BTC may drop by 20% while another alt goes up by even more.

Basically I don’t think this proposal is a cure all solution to the issue you have raised. Mostly because you have a wrong diagnosis of the problem.

But I still like the idea of more direct exchanges.