I don't think lucky blocks mega would work well. The mode would require a really large maps with enough lucky blocks for everyone on each team to comfortably get a few of them. On top of that, because of some deadlier lucky block drops, a mode like that would rely on RNG even more than the other modes because, if you were to get unlucky, you could end in a situation where your team has 4 players left, the other 6 died to bad lucky blocks, and the 4 remaining all got unlucky with gear, meanwhile you got a team of 10 approaching, all with shining enchanted gear.
I know that lucky blocks normally also relies on RNG, but a 1v4, or 1v1 is generally speaking much easier to fight than a 1v10.
I do not see any reason not to add duos, though.