Why do we keep saying tic-tac-toe? It reminds me of bingo, but with 3 per row
I think the stacking's one of the most important aspects. If you can get your robot to hold the tetras relatively stable-y AND stack while collecting (go in and out of the loading zone, collecting more than one tetra and forming a stack before you put it onto the goals) ... you've got a pretty good advantage there.
Then again, they're pretty heavy to keep holding.
And I have no idea how such an arm mechanism would work.
.. But anything's possible!