The Infinite Crisis website has word that this DC comics-inspired MOBA will launch on March 26th, and that the game will be available on Steam that day, though this will not be required. Here's a bit from the FAQ on what this means to existing players:

Q. What does this mean for us beta testers? Will you continue to update the game?
A. For you, our existing testers, there won’t be a significant amount of change. You’ll still log into the game with your existing WBID and your account will remain the same as it’s always been. We will continue to update the game with new features, Champions, Costumes, optimizations, and plenty more.

If you want to play the game on Steam, you’ll need to uninstall your current version of the game and re-download it through Steam starting on March 26th.

While you will still be able to play the game through the existing launcher, we do recommend that you uninstall the beta version of the game and play through Steam on March 26th in order to take advantage of our Steam features, including Friends List import, Steam Overlay, and Trading Cards.

Q. Will you be wiping my account or removing anything from my account?
A. Nope! When we said there would be no more wipes, we meant it. All Champions, Merit, Costumes, Crisis Coins, Friends, and everything else on your account will be available. You earned it, after all!