It wouldn't surprise me if they were to introduce an entirely new faction. GW does have a good amount of IP to draw upon.
Personally, though I'd want Kroot to flushed out (again). A mercenary type army that selectively mutates, but could have more individual character than Tyranids. Done correctly, they could be a really poor man's version of deathwatch for xenos. Their wargear would just be options from other races. Then add some tribes/clans evolutionary traits, and BAM! This would also setup the inevitable Alien v. Predator memes (again). Unfortunately, I don't see many new range refreshes for xenos on the horizon given that Necrons just got one (I'm not saying they are not needed).
I don't see Tyranids getting a range refresh for at least 2 editions. Necrons were just released, so next non-Space Marine will probably a chaos, maybe a traitor Primarch (Angron or Fulgrim [VALRAK incoming]) and maybe Tyranids.* I only see them doing Tyranids after the Silent King kills a hive fleet and they need to adapt (for a couple of editions).
That puts my hopes of a true Kroot army to 2024.
*Space marines assumed to get new stuff every time a different factions gets at least one thing**
**Thing can mean, but is not limited to: rules, models, white dwarf articles, warcom article mentions, a favorable tweet by a GW
employee, a trolling mention on the whiteboard of a GW
employee, the sun rising, the sun setting, overcast conditions that negate visibility of the sun, a nuclear winter
Edited by Reigart, 16 October 2020 - 03:35 PM.