I should've worded it a bit differently, as directly accepting Bitcoin would surely accelerate adoption. But just being able to quickly liquidate your assets by "directly" being able to purchase real goods with your assets (even through a middleman) is something that was and is not possible with traditional assets.
Thus a wide spread acceptance of cryptos (even through a middleman) would offer a completely new merit to cryptos as a form of asset that stocks, ETFs, bonds, etc. do not have, since you first have to sell them to be able to use the money for anything. And that can take several days to weeks in some cases.
I think the problem nowadays are commissions. I have only been into bitcoin a couple of moths but when I get information about the past years I see that commissions were pretty insignificant whereas nowadays I can pay a 0,70 coffee with my mobile and if I had to pay it with bitcoin I would have to pay a commission, not so insignificant in terms of percentage.
I wouldnt be surprised if bitcoin is used just for big transactions in the future and as a store of value, but it coexists with another alt for small transactions.
Yeah, that's what bothers me about Bitcoin as well. The high transaction fees. I used to order pizza and other food online regularly, but now the fees are about $4 per order... which is 25-50% of a meal. Hopefully a few forks will resolve this issue.