This is interesting. It's happening in baby steps, but we've now got one Touhou game released on an english site, one doujin game released for PS4 getting localised and an official Touhou game preparing to get ported. It's a short step from there to an actual official English localisation. Which may not happen, but from what I understand the obstacle preventing mainline Touhou games from getting localised is really just that ZUN would prefer to work on something new that go through the old things with external partners. That may not be such an issue for Tasofro. Of course, if the issue really is with localisation itself then it's a moot point.
Idiotic character speculation follows, feel free to ignore:
I'm fairly sure the characters that go into the game go in for gameplay reasons, not story reasons - the scenario is then written from that base. There's also the drive to provide characters from a broad section of the series, particularly the current era and specifically characters that haven't been included in previous fighting games. IaMP and SWR came with the first windows trilogy, so as Hopeless Masquerade was a fresh start as far as sprites were concerned it contained a broad sample of characters from the more recent games in the series - one from MOF, one from SA, two from UFO, three from TD. That's why you had characters like Nitori and Koishi in the mix, they represented the modern Touhou era and hadn't shown up in the fighting games previously. ULiL just expanded the range of games that were being drawn from, adding in one character from the most recent game and one from the game (excluding PoFV as a competitive game itself) prior to Mountain of Faith.
If adding characters is what they're doing (and that's pure speculation at this point), I'd anticipate a Legacy of Lunatic Kingdom character, maybe an extra one from Double Dealing Character and maybe even one from Perfect Cherry Blossom if they're working backwards as well. I'm not sure who they could add from PCB though unless it was a character who'd already appeared in a fighting game, all the cool characters were in IaMP. If there's that the most recent trilogy is about though, it's reconciling the characters and settings of the earlier windows games with the gameplay of the more recent ones. So it wouldn't be completely out there.