Hi, sorry for the late reply I am currently working full time in C++ on a different project so didn't check Genome2D forums, my bad. It doesn't mean Genome2D is abandoned it just means that sometimes one needs to put food on the table from commercial projects. :)
Anyway to your question, GSlice9Sprite, GSlice3Sprite, GTiledSprite are being abandoned in upcoming update in favor of the more customizable slicing that was introduced in the UI part of Genome2D. Basically you will be able to do any kind of slicing with it not just 3/9.
If you want to check out the slicing code just check out the GUITextureSkin.