Now, that’s interesting. I don’t think the wetlands planet would make a good ending - episode 3 would be strongest this way - BUT you could use the wetlands content as the Mando opening in your second movie. Boba’s with tuskens thinking he’s found his people, Mando’s with the wetlanders wondering if he can find peace. Boba’s tusken family is killed, Mando gets tracked and has to leave his wetlanders. That segues nicely into Mando being pursued by the bounty hunter onto Tattooine, before the Fennec storyline overlap. Gives us a bit of a break from too much Boba/desert too.

It would also nicely set up movie 2’s conclusion - an opportunity to finally stop being pursued, which we’ve now seen happen to him heavily emphasised in one movie.

Edit:

Ah but wait! This means you wouldn’t be able to use wetlands to close out the flashback content. Ach!