This was true for a long time, but we do actually have a bootstrapped openjdk for arm since a few months: https://github.com/NixOS/nixpkgs/pull/65247

(I package sage for nix)

The problem is that sage actually depends on Octave, Maxima, R and many other packages. It parses binary output of many dependencies and often needs the exact version it expects because of that. It also has relatively brittle doctests testing everything an as a result often breaking on minor changes in dependencies.

If you have too much time, there is a very lengthy discussion on this on sage-packaging: https://groups.google.com/forum/#!topic/sage-packaging/ZJmJZ...

I recently started using Markor for that purpose. While it wasn't built as a vimwiki client, it is good enough for my purposes. Some info at https://github.com/gsantner/markor/issues/317.