And now that Lion-O's stated goal is to unite the different tribes, there's the very interesting question of how THAT will go.
There are obviously Lizardmen who aren't totally onboard with Slithe. Will they splinter off and join with Lion-O?
Or, more interestingly, will Slithe recognize that, with Thundera destroyed and Claudus dead, Mumm-Ra is the greatest threat to him, and switch sides for a temporary alliance with the Thundercats? That would be a lot more interesting than the standard trope of serving Mumm-Ra while plotting against him.
Also an option: Lion-O unites the Mutant factions -- against himself. The first episode of TOS made it clear that the three Mutant races working together was completely unprecedented, and I always wanted to see more of that. The rest of the series certainly played a lot with the idea that the Mutants' (and Lunatacs') greatest weakness was their inability to cooperate, but it would be neat to see what they could accomplish if they actually COULD.
Long-term, the series has to converge on #1: Slithe's not going to reform, but ultimately you HAVE to have the Thundercats unite with good-hearted Mutants, because otherwise you're left with something cynical (that also ends up promoting the same racist undertones that the series has taken great pains to flout). But short-term, I'd be interested in seeing how the other possibilities could go.