Welp, I'm considering three things:
1) At least one new amiibo, and some new gear, seems likely due to code from 2.4 and the appearance of box art for a new arcade game in Ancho-V, meaning it's reasonable to expect one last update
2) The Research Lab called Ancho-V the last map rather than the last content. Smash made sure to tell us that the February DLC will be the last new content for the game, so why not do the same with Splatoon?
3) Nintendo knows they have to end this with a bang. They won't just be like "Hey, remember that map you got last week? That was the last content lol bye"
So I'd say there's still a possibility. I still haven't heard a good explanation for why the Octoling models were updated so much (Why update them at all if they're just used for Single Player anyway?), and I can't see the time, money, and work that went into updating them (as much or little as that may have been) going to waste. I suppose there's no way to know until the month is truly over ¯\_(ツ)_/¯