It both doesn't make sense and does. They've definitely been trying to move Casas most of the winter (Cortilo and McAdams have been saying as much virtually every pod since the winter Meetings), and as you point out, we've seen the Mookie play before. So they could either be asking for little money back and an extra player on top, or attaching Yoshida (which out of everything feels the least likely).
Again, I just don't see it, but an infield of:
1B Devers
2B Bregman
SS Story
3B Arenado
Certainly makes it a plus. With Duran, Raf and Abreu in the outfield, the defence would suddenly be a strength of a team that has had none for a few years now.