H-back/flex tight end
It's not often where I get this stumped on which position a player projects to best. However, Thomas can truly do a lot of things, and at a high level. But watching how naturally he plucks and tucks the ball out the air, runs like a dear in the open-field, and shows the willingness to block, he might provide the most immediate impact at H-back or flex tight end.
But then again, it's usually a quicker transition to defense as players are enabled to react and just play the game a bit more than they are offensively.