given that the game is a re-make of an existing game -- the content of which is now forever set in stone, and includes Ada's missions, as well as more Mercs maps and characters -- one might have been forgiven for thinking that they'd have given players a content suite that was something approaching what was in the original game (instead of waste-of-time, useless "collectables"). That, and Ada's no adjunct character -- her role is crucial to the plot: to not include, at least, one of her side modes, or even just her as a character's presence in Mercs, smacks of both laziness, as well as rank self-assuredness -- that people would buy the game irrespective of what they gave / didn't give them / left out (their target demographic likely wasn't even series veterans).
If I were in charge of the re-makes design team, I'd have stipulated that they add, not only the original's Ada content; but, also asymmetrical co-op functionality for Leon and Ada's intersecting campaign (think: RE6's similar functionality)... To make the product a genuine upgrade to the original, and not just coat-of-paint cash-in on the seminal title's reputation. But, that could just be me...
NB: They released no DLC content for either the RE2 or RE3 re-makes. By that measure, the chance of them bringing RE4 re-make to something approaching a complete state, is somewhere between Buckley's and snowflakes. If they intimated that they "might", they're all but guilty of false advertising. Owari da.