>> Slug only needs to render a quad for each glyph.
I don't know how many glyphs you want to render (to the point that there are so many that you can't read them anymore), but a modern GPU s are heavily optimized for triangle throughput. So 2 or 20 triangles per glyph makes only a little difference. The bigger problem is usually the sample fill rate and memory bandwidth (especially if you have to write to pixels more than once).
I have been eying the scanline-intersection-sort approach (your third link) too. Sadly they have no answer to path stroking (same as everybody else) and it also requires an efficient sorting algorithm for the GPU (implementations of such are hard to come by outside of CUDA, as you mentioned).