So, I came from a game called “Marvel Heroes”. Over there, they have something called the “Advanced Pack”. It’s literally $100 for every character coming out that year. They set up a road-map of what they plan to do, and release characters based on that plan. While I realize that this would be hard to do given that you’re creating the Mercs yourselves, rather than pulling from the lore of a comic book, it wouldn’t hurt to throw groupings of the mercs that are waiting release into $20 grab bags of 4 - 5 of them.
Given you have like… what? 17 wait? That racks up to $60 - $80 with the current 5 and the rest you have yet to release. Make an Ultimate Pack for $50 for all the mercs that have yet to be released from beta test, and honestly? Yeah. Pretty sure everyone in the game would have them.