All the novelty $1 coins since the Sacagawea offer the potential for a gradual shift too. Modern multi-denomination coin mechs are likely to accept them, unlike the Susan B Anthony's that were too close to quarters [1]. Some of them even have a sticker near the coin slot advertising the feature. So if someone has given you a dollar coin in change (probably a government cashier or machine), you might be able to use it in a machine. I couldn't find a well reported number on dollar coin acceptance --- just an undated claim of 30% of machines accepting them according to Vending Market Watch but no link to an article or anything. I did see an article on VMW from 2011 about cash recyclers that allow a machine to take a larger bill and issue change with smaller bills rather than only coins, that featured a quote that resonates with me:
> "Customers have told me firsthand how thrilled they are to receive bills as change instead of dollar coins," said Mike Gallagher, service manager for Coca-Cola Bottling Co. "Sales on those machines have increased, and the technology has been extremely reliable." [2]
[1] I did see one coin mech in the wild that took Anthony dollars; but it was a spendy arcade game and had a dispenser next to it to get the dollar coins you needed from bills or quarters. And there were big signs about it, at the Disneyland StarCade in the 90s.
There was always a potential, but without a plurality of momentum, they're not going to replace their predecessors. The early 00s was the best chance for this, in the wake of the Susan B Anthony reissuance and the new Sacagawea dollar, when there was a decent amount of public interest, but as it turns out, anything less than 100% acceptance is just not as good as the 100% acceptance of quarters in coin machines, or dollar bills in bill readers. People won't use them if they aren't accepted, and retailers won't accept them if they aren't used.
That's a very different thing in terms of switching costs than an immediate switch that demands replacement all at one time.