I don't disagree, but this takes seconds instead of 2-3 business days in the case of ACH verification. 2-3 business days is an absolute eternity in the world of Bitcoin speculation.
You can do what Gemini does -- credit the account with fake money once the user requests ACH transfer, let them make trades with it, and only let them withdraw any proceeds of it (whether bitcoin or fiat) once the ACH transaction fully settles.
