I would see that if rathalos was just an assist trophy, but given that it actually has its own boss arena, I reasonably expect we'd actually get it's theme. Granted, becuase it seems to be a boss only-stage at the moment, it could very easily be just Rathalos' theme and nothing else, and, if that is the case, it's an interesting situation of a third party theme without an attached fighter or group of songs (at least all the namco medlies could get grouped with each other).
Though, if somehow Rathalos' arena is just an alteration of some as of yet unseen smash original or other franchise stage (I doubt it because I believe it's been identified as being a location from monster hunter, but you never know), then it could indeed be without a theme. Or, maybe it will perhaps get a generic boss theme if such a song ends up happening, though it would break brawl's tradition where bosses from other games did get some music from their home series.
EDIT: On an older post i said we were on six songs left, I miscounted. We are on seven songs left and after tonight’s goes up, that’s when we’re on six. In hand with that, I propose we’ll get a mix of these songs (obviously not all because combined they exceed seven)
Used on website series: Mario, Zelda, Kirby, Pokemon, or street fighter (last one is just due to sheer number of new songs and having had on on the website since day 1. The rest could be for potential newcomers).
Unused on website series: star fox, Kid Icarus, Wii Fit (maybe odd choice, but it has at least 4 new songs for ultimate), and one of either Mother, Xenoblade, Punch Out, Wario, or Sonic (based on reusing series plus new franchises, plus more likely unused franchises, I feel like the odds are only one of these smaller more “niche” series get a song on the site,and sonic is forever tricky)
Probably at least one new franchise for smash, maybe even two. If nothing else, one more “other” to fill this category.
Lastly, a smash original song: either a remix of an older smash theme or a song for the hidden mode.
Also, the way i figure is, we’re likely to get a mario/Zelda/Kirby/Pokemon/newcomer franchise song or three after the direct, depending on new characters, and I think the smash original song/remix will be the last one before release (if it doesn’t go after the direct that covers the mystery mode). For the non-post direct/right before launch days, I see mario, Zelda, and maybe even street fighter if they get no new characters, and the unused series. In the case of Kirby and Pokémon, I only see a new song if they have new characters. Lastly, if we don’t get a new franchise, I can see an “other” on one of those off days
Though again, I probably should stress, that’s more just the pool I think can be pulled from. Given I have at least 11 possibilities one mind (5 used, 4 unsued, 1 new franchise/an “other” and 1 smash original), while we only have 7 left, obviously not all can make the cut.