To parrot my own comment on Reddit, the multi-launch is the current leading rumor, yes, but Coliwoods didn't really give his opinion on that rumor's validity. The first source for it was TPP, whose record is... well, I like to call him Theme Park Wishlist because I feel like it's more honest.
$15M isn't too crazy in coaster terms, but if SFGadv wanted a coaster ready for 2024, they'd probably need to start clearing the arena soon. Like, before Fall. Also, if this is true, and the old Giga rumors are true (particularly the part where Selim cancelled it), that means they had very little time to plan this. I suspect Gadv might "just" be getting a west coast racer clone, or something equally "low effort".