So, Wallaroo is a source-available project. There IS a term for this sort of license, and it isn't "open source."

You're just mincing words. The author(s) is upfront about the source distribution and licensing and is not being misleading, as the GP implied. I'm really not interested in yet another discussion about definitions when the author's meaning is perfectly clear.

If you ever feel you need a phrase and "a phrase" in the same sentence, chances are you won't come across perfectly clear. You are then either implicitly contradicting yourself, or bringing in a statement about your perceived validity of the very same statement you choose to use into your writing. Whatever it is, it's not clear writing.

Hence, I would say that the meaning really isn't clear, especially not in the context where it's stated. This lack of clarity is further bolstered by the blog post linked from the project webpage where they mention it's going to become open source, there they spend a fair amount talking about exactly once delivery and how important it is. It turns out that exactly once is not a feature covered by the Apache license.

Almost every project containing both for-payment parts and open source parts split them into separate repositories, it's a good practice when there are different legal agreements involved, and I see no real reason for not splitting it up, except possibly that pony might be one of the opinionated languages where you can't build things if not everything is in the same folder?

If that is the case, those constraints are - as in go - rather shortsighted. The world is a complicated place, simple solutions rarely work as well as one might hope.