Looking at http://www.lysator.liu.se/~nisse/nettle/plan.html, the most important things are done. I think documentation is the only item left which is both important and requires several hours of work.
* Versioned symbols. I think this is complete, I just have forgotten to merge that branch.
* Base64 with other alphabets. A patch was posted to the list some month ago, I had some comments, and then it seems to have stalled. If it's desirable to break the ABI to implement it, 3.1 may be the last chance for some years time.
* OCB mode. Is it a good idea to try to get this into the release? I don't think patents are a problem, but I've mailed sflc, and it would be nice to get their opinion too. Needs not just the code, but also test cases and documentation.
* Also OFB mode has been requested, used by openpgp, iirc.
Anything else I've missed? And which of the above items are important?
There are a lot of things that could be better optimized, including the curve25519 code and the aesni code, but I don't think the release should be delayed for that.
Regards, /Niels