Hard to predict, how?

When most retail is on the Internet, then the whole retail sector becomes a natural monopoly.

Given that neither R nor D has shown any inclination to enforce anti-monopoly laws, Amazon will simply take over all of retail except a tiny segment of boutique businesses aimed at the rich.

Another faint possibility will be that another large competitor emerges in the retail space. This would have to be WalMart, perhaps together with other dying retail businesses. WalMart has shown strong competence in online sales, with solid integration with their brick-and-mortar stores, so you can't count them out, but given Amazon's almost perfect execution on their plan to take over the world and their substantial head start, it seems like a long-shot.

Regardless, there won't be anything at all like the diverse ecosystem of retail at all sizes that we saw up until 2020.