I was worried we were only getting Four DLC characters for Injustice, as that's all that's been announced and Mortal Kombat 9 only got four despite promises of more than that if sales were good (they were VERY good, too.)
But, having just received Lobo... I have a new theory. NRS set a very specific deadline for the Season Pass of "All content by August", which seems odd for them if it's the only DLC they outright plan on. On top of that, Ed Boon has said "I definitely can't say with any confidence these will be the only DLC characters." Having downloaded Lobo... they've added him to the "Heroes" side of the roster, as a fourth character on the bottom row... Batgirl is also a "Hero", and Zod and Scorpion will be "Villains"... That's two added onto each side, making a new half-column each.
Stands to reason... they're going to release a season Season Pass to finish up those columns.
I wouldn't have specifically thought this if they had done what they had with MK9's DLC (a fold-out row), but this is actually forming new columns, and there is exactly enough room for eight characters.
So even though we're definitely getting Batgirl (and most likely Scorpion)... we could be seeing a future of a lot more characters, and hopefully some of the more highly desired ones.
Lobo is awesome, by the way. Definitely worth the download.