And furthermore, introducing the Hyperclan at the same time as you introduce the Justice League is just too many colorful costumes to keep up with, even for me, an avid comic booker.
With some tweaks, the white martians could be really good. So what they're not martians? Americans aren't even Americans, but rather, a foreign race that conquered America a long time ago, then went to conquer Iraq. And our designs are EXTRA lame.
However, I think for a big ensemble cast like JLA, you need a single epic villain to focus all around hate... you need our Sauron, our Agent Smith, our Emporer/Vader, our main big bad, under whom all our other challenges can fall.
But the White Martians lack a single charismatic lead.
I think Despero is a character that can give the whole JLA a run for their money.
I think Darkseid can have the 4th world as a byline and flashback rather than his main plot and be a great foe to the League.
With the right other things going on, Vandal Savage would be a great villain, especially if he were the one to orchestrate the Injustice Gang, something which can be pretty corny and unbelievably hokey if not done right.
I think those four are your best bets... the JLA has tons of villains, and often borrows main villains from Superman and Batman's rogue's galleries, but I think those four have the most potential overall.