Nova didn't (doesn't?) work like that, no, but Nova had a different vibe intentionally; it's geared at a different pace. Much more detailed around a single setting where each person plays one character in a lot more depth, e.g. half a dozen people writing a different role each on a spaceship venturing into deep space. Would be weird to see a Nova install with people writing even 2-3 characters each from what I saw.
One thing I will say, I actually intentionally set up StoryBB to have you switch personas when posting because I originally thought on a site where people played maybe max 5-8 characters, they might pick a theme to suit the character (e.g. the original site it was built for was a Potter RP, and there was a light/dark theme plus one for each of the Hogwarts houses). It's funny how wrong that particular factor ended up being, but people do seem to like actually switching characters before posting to get them in the right head-space.
I did consciously make it easy to move posts between characters if you got it wrong - it was never more than a click away (didn't even need to edit the post), and we also made sure the Discord notifications didn't go out immediate to allow people a minute or so's grace to fix obvious issues before it did that.
Personally, I've never been a fan of the dropdown-at-post-time, seems far too easy to me to post as the wrong character. I sometimes wonder if this is because of the different numbers of characters we play - I only play 6 at present - but the joy of RP is that everyone can absolutely find the place and pace that works for them, and you seem to have found yours which is awesome.