I'm being a little reductive here, but what I'm saying is that a lot of Jetty-Syns' behavior could carry over very easily with some small tweaks and a change to his missile-spawn. Spinies themselves could very easily draw code from the spincushion/sharp enemy. I could think of at least one area where a Lakitu might fit (and it would only need to be one).
That was just an example though, and I'm not intending to apply pressure; I've had ideas for like half a dozen Mario enemies, from paragoombas to cheep cheeps. I can understand why nobody's invested resources into it yet (new sprites and all), but the actual coding and implementation of those enemies wouldn't be that difficult.
Well I am not saying that could be really difficult, but I don't think it would be really worth it to put into "pipe tower" section(well area after starting area is also suitable, but there would be problem with staging, like out of nowhere there would be already 3 enemy types, I rather like to introduce in some fashion Lakitus than throwing them into 1 section). I also like my enemies being at very least in half of level.
Though I kind of in development got ahead with stuff, I wanted to implement winged type of existing enemies with papersprites, but I gave up on that and focused more so on map itself really.
Hmm... there are a few, minor things that prevent this map from being perfection for me:
1: Breaking brick blocks doesn't add to the score.
2: A lack of emblems.
There is another thing, that is somewhat irritating, that being that there doesn't appear to be a 2D mode, but that was honestly the old Mario Koopa Blast's thing, and not Pipe Towers.
Though, it would be nice to have a castle section in a later version of the level...
1: Well we wouldn't be exactly able to add 50 points reward for breaking bricks, that's more so vannila's mario block linedef special problem.
2: A lack of emblems is more so problem with Gamedata situation itself, Emblems are already placed there. Unused SOC for Emblems is also there.
I even wanted to make custom Gamedata, but we decided that without making Pipe Tower zone map01, we rather go with generic option of not having custom Gamedata at all. Of course you can enable them if you desire :P.
Uh that extra thing how it can be irritating ? MKB Demo4-2.0 had first act also 3D only, only act 2 and 3 were recreations of mario levels in 2D. And it is more so, because Sonniku and SSNTails were messing around with Mario ideas than anything concrete.
Well I actually attempted to do castle section at one point as Knuckles path, but I ended it up scrapping it, like we felt we were over doing it. For same reason we won't add any more sections into map itself.
Main point of entire pack WAS to make assets useable outside of Mario mode and bring them to some standard unlike them being upscaled versions of Super Mario Bros All-stars, 1 and World's sprites and tiles. But they didn't exactly fit Pipe Towers zone (that doesn't say lot, because not even current mario textures doesn't fit original at all), so I had to rework entire level, just to make them fit and them being good example for their use and also I tried to elevate some issues and we added some additions team wanted to add, when I was at it, which ended up being this product as whole, like I didn't expected this will turn into something more than just asset pack. TL;DR Anyone is free to do castle level with assets available there, due to this being "re-useable" content.