You mentioned DHing Moncada part time in previous posts as well. I think you're trying to out think yourself. In the 40+ years that the DH has been around, I've never seen a team take a young, athletic, highly touted prospect and DH them, part time or not.
Moncada & Swihart are two of the best athletes in the organization. They need to play a position every day, not DH. It'll never happen with either one of them next year.
Then there's the whole additional mental aspect of trying to DH, play multiple positions, etc. A team like Boston, that puts a ton of resources in training players for the off the field part of the game, isn't going to impede a top prospect's development because they may need a part time DH, 3rd catcher and 5th outfielder on the roster.