Thank you! I'm always glad to read that I managed to create something that people enjoy. I'll do my best to make a worthy next version.
Unfortunately, adding the option to play with the original green soul mechanic probably would be a bit time consuming, as it basically would mean adding a completely different soul mode and I'd have to create dozens of new attacks for it, since most attacks of the 360° green soul are not meant for a shield that snaps instantly to anywhere you want. So it's most likely not going to be a part of the version 3.0. That said though, the new version will add modifiers that you can enable, so that you can customize the fight a bit more(things like game speed or undyne's hp and damage and a few others). I can see a possible future modifier for the original green soul mechanic in a 3.1 version