this is still in dev ?

I really don't like necroing this... especially cause it's not really an issue, but... is there a chance that this will get revived and ported/remade for current versions?
I'd love to have something like this on my spigot server and was unable to find anything even remotely similar.
Would also be able to provide testing and compensation if necessary.

I wouldn't mind doing it, but I'm still strained for time (and I would do a proper rewrite for modern MC, I also have lost access to the original account that published it). But it seems someone has put some effort into it: https://dev.bukkit.org/projects/fixed-code-for-blueprint-builder

No worries, interest in my community has died down quite a bit, so we're not gonna get any complex builds going anytime soon. FYI tho, the fix/patch you linked does not function with current Spigot versions. (last tried it on 1.19.0, I think)

Unfortunately not really busy with university work and the entire DMCA event a while back, haven't really gone back since then.