What's a word for someone who pushes boundaries and things forward that is positive in connotation?
push the envelope: exceed the limits of what is normally done, be innovative, as in They are pushing the envelope in using only new fabrics for winter clothing.
By extension, I think you can use envelope pusher.
In addition, you can try:
pioneer: one who opens up new areas of thought, research, or development
pathfinder: someone who discovers and tries new ways of doing things
Wiktionary: Transcender defines a person who transcends.
Transcend means to pass beyond limits.
[Cambridge dictionaries] a person who thinks and acts in an independent way, often behaving differently from the expected or usual way: