I'd be fine sending both Davis and Ashcraft, though generally I don't like the idea of punting on Davis after so few ABs given how bare the hitting prospect cupboard is. But if you can make that swap, you solve a need and don't tap too much into your depth.
I don't quite get the angle for the Marlins, though. I suppose there's some more certainty about both guys as they are closer to MLB ready, but the Marlins look to be a total that is ripping everything up that it can. They will be in a race with the Rockies and A's to try and secure the highest lottery rights, and then they'll do the same thing again next year.
It makes more sense for them to be looking at guys who have high ceilings but are 2-3 more years away at least.