Open source generally builds slowly. It takes time for communities to coalesce around new tech in ways that are meaningful. It is worth the effort and time it takes to keep the software updated.
For faster feedback on the core ideas, a paper would serve very well. You'll have the attention of your peers and the faculty to gather initial impressions.
There isn't any reason why you couldn't do both. Open sourcing new ideas doesn't mean you cannot write a paper on the subject. The code is still your idea at the core. Refinement of the code doesn't change that fact.
Great points, I think I may be overestimating the speed of Open Source development in my mind, leading to the mistaken assumption that all my time should be used rapidly building better tech. If that isn't the case, and there's bound to be a slow uptake on the OS side, it certainly seems prudent to shift my attention over to communicating and disseminating my work, perhaps through a paper.
Open sourcing your code is a way of "writing a paper" -- it's a way to get it out there.
One paper rarely does anything. Likewise one repo. Certainly each can point to the other which may help someone else to understand what you were trying to accomplish, and hopefully build upon it.
Regardless of all of the above: making a public repo with an open source license is a good thing to do if the alternative is for it to be dropped. Back in the early 80s I wanted to see some code written by one of my advisor's prior students (for his PhD) back in the late 70s. I had to send him email to Sweden, where he had since gotten a faculty position, and he sent me a tape! His code was no longer on MIT backups. All this for what turned out to be me reading a few functions our of his implementation that explained something I hadn't understood in his thesis. Had I known, I could have just asked him the question. Or today, looked at the code on GitHub.
I think you may also get some satisfaction in writing up your work. You can store the paper in the repo as well, of course, in addition to submitting it to a journal or giving it at a conference.
If your technology is patentable, you may want to patent it and then put the patent in the public domain to prevent it from being patented by some other person. Public disclosure does much the same thing but filing a patent is much more effective.