- Really try hard to optimize the Huffman decode table generator. SIMD it, whatever, it's way more important than I thought.
Various things I tried that didn't make it into LZHAM1:
An effort like this would make a huge impact across the entire web stack. The gain would be relatively massive compared to the tiny improvements Zopfli's been able to achieve (~5% for 100x increase in cost means it's time to move on).
If the new codec is made zlib API compatible (like I do in LZHAM and miniz), which is easy, then dropping it into existing codebases would be fairly straightforward.
It could support various executable formats (dwarf, exe, etc.), xml, json, html, jpeg, mp3, wav, png, raw images, deflate, etc. All the best archivers already do this and the research has been done, but AFAIK it's not available as a single robust library.
With good parsing it's easy to add more node types to the parse graph. Right now I'm adding only literals (which are coded in various ways depending on previous state), and various matches and truncated versions of these matches.