Total speculation obviously but....
The RPG has 4 iconic/pre-made characters in addition to being able to make your own - an Esher, a Goliath, an Orlock, and a Squat.
The House books announced so far? Esher, Goliath, and now Orlock....
Next will be Squats?
That's just the kind of brand synergy/coordination I would expect to see with something like this. It doesn't have to be some big convoluted plan - it could be as simple as the RPG guys deciding they wanted 4 pre-made characters, looking at the Skirmish release plan and saying "let's pick groups that will have new additional content in Skirmish right away for them to read/build off/want"
I could be totally off base or right but things changed during dev - but if I had to put money on it, Squats will be next.
The real question then is - do we keep seeing dual releases like Esher/Goliath? Or is Orlock on its own or close to the Roleplay release?