Touch- or remote-thawing a thawer would have no effect (as it does now).
But I would have it so the speed at which player 3 thaws is always one 'thaw speed increment' slower than the chain link in front of him.
So, only if player 1 and player 2 were thawing player 3 could player 4 be thawed by player 3.
Aaand, if player 4 is then thawed by an additional teammate, their and any subsequent chain would increase their 'thaw speed increment' by 1.
Essentially, any thawee may replicate their thawing speed minus one 'thaw speed increment' to another frozen teammate by remote-thaw.