Why trade for him now. We can't fit him in and we have the luxury of waiting until the end of this year to see how Goff pans out, how Cousins does with new receivers, etc.
Detroit doesn't make much sense either. Is he an upgrade over Stafford?
The San Fran thing could happen - they might have the cap room to add him now.
Denver is also a good fit - though I doubt they have the cap room.
I guess with any of these - Cousins could sign a long-term cap-friendly deal. I would think that Denver would be the preference as they are built to win now. If he goes to San Fran or LA - he's on teams that are still rebuilding.