Reading all of these trade scenarios and what it would take, and then adding in the cap ramifications makes me think it would be far better to just improve the damn OL and roll with what you've got. It would certainly be better for the people that decided to extend Goff just two years ago. Not to mention, the cost of getting Watson now would make it all that much harder to put a competitive roster around him, OL included.
Last offseason they prioritized defensive signings in FA and positions other than OL in the draft on the theory that they could fix the OL with the players they already had. While the OL was improved over the '19 season, it still wasn't good enough, and teams exploited the weak links (especially Blythe) all season long. Giving up a crapload of talent and/or future picks for Watson now is only going to make it that much harder to get the OL up to where it needs to be - and where it was when there were few if any questions about Goff as our QB.
Fix the OL, and upgrade the scheme and the playcalling. If Goff still is regressing in that scenario, then at least we go into the '22 draft with a first rounder and the possibility of getting someone or moving up.