The next gamemode, osu!dodge, has an estimated date of arrival of TBA, and it has been like that for several years. Peppy is currently busy reworking the graphical aspects of the game, managing the creation of the new osu! website, and is working to open source the game. I think it will be a while more before we get to see a new gamemode imho.
I am not sure how into this game you are to suddenly get a mind set of programming something for osu!, considering your play history. I have poured wasted hours into this game, not sure if you want to do same. If you are still up for it, then your only option right now is to develop 3rd party software for osu!, as you see in this subforum, or do some web dev/design for the issues marked with bounty
here.