The code for maiden (the norns editor) will be released with the shipping of the first batch (along with all the other code).
If one is looking to experiment with Lua in advance any editor will do (gvim, emacs, sublime, VS Code, etc.). The primary distinguishing feature of maiden is that it is designed to be run (served) directly off norns and provide interaction with matron (the norns Lua engine). As an editor maiden is fairly minimal.