I think three important things are missing in NetMQ (or netmq family) without currently a solution, from most important to least:
1. Universal Windows Platform (UWP) support, I have started working on a small library, but it is unfinished, if you want to take the lead it will be great:
https://github.com/somdoron/ZMTP.NET. Mainly it doesn't need to support all of NetMQ features (or performance) just simple implementation of the ZMTP procotol will all relevant socket types.
2. Better Unity support, here as well I think we should small portable library instead of trying embedding full blown NetMQ in Unity, anyway NetMQ and unity is not working perfectly at the moment. I think eventually we should have ZMTP support all frontend platforms and not only UWP, which will also solve Unity problem.
3. Security, ZeroMQ v4 and ZMTP v3 introduces security features (based on NaCl). NetMQ need to catch eventually. I will start with supporting ZMTP v3 with null mechanism, we can then introduce the curve mechanism. There are number of NaCl ports for C# , I also created one, but it is un-maintained and not ready.
Anyway, I think the first one is the most repeated one. So if you can take the lead I will move the project to the NetMQ organization and can help you with direction.