While we did not directly create a Save As feature, we have now added a Copy feature which works nearly as well
One thing to note is that copying the song will only copy saved progress, not any unsaved progress. We suggest making copies as you save to create in progress versions of your files.
This feature can be found on 5.0.x!
I will for this reason tag this as #implemented even though it is not exactly what was requested, it satiates a lot of the requests needs
Thanks for all the feedback!
I will also point out that the loop limit is now way more than 2:30 per part as OP posted, and has been since version 4.0.x