Even with the their latest release of Wasabi Wallet, the changing of a coordinator is as easy as clicking the settings icon and pasting the URL therefore control over the coinjoin function stays with the customer. That was also the case in the previous version of Ginger Wallet via editing the config file but what seems to be the case in their latest release the
config file reverts to default without saving the settings on restart.
What that means is if you use Ginger Wallet you have to use their coordinator and pay their fees when there are free alternatives out there. On the surface, what it also means is that if the service does go down it really could be a case of bye bye for those using Ginger Wallet if their settings are not allowed to be altered. The current way around it seems to using an earlier version or using Wasabi Wallet (not running both clients at the same time).
You are right and not only specific to these wallets but in the general sense at least with any software, if a form of universal API was agreed upon by various developers (that forked a single source code for their own releases) it might alleviate any problems switching if any one URL was unreachable because a domain expired or a business decided to shut down as it was not profitable.
I think the reason for these designs being so brittle compared to let's say the Bitcoin protocol itself is because the development team assumes their program is going to be the only one functioning with this sort of API, such that in case the service does go down (like Samourai), it spells death to the API they're using as well (bye bye Whirlpool).
If people see that there are other teams with forks of their software and they still use a similar sort of API, they should at least try to reach out to the other teams to attempt to coordinate a common standard for the backend/API or whatever is behind the scenes so that users can easily switch from one to another. But that's hard to do unless you gather all these people at a Bitcoin conference.
