Again if they go this route, there is zero reason to do full cgi/mo-cap:
The hulked out designs in the comics of the pre- and post- Annihilation Thanos were rather silly anyway. A reasonably proportioned design with an actual neck would work muuuch better in live action. They can use tried and true (and cheap!) techniques to make him bigger in proportion to the human characters. Maybe some cg touch-ups in post. Why even bother with mocap?