I will work on merging the Link part of my branch to upstream soon.
The 0.19 conda AppImage theme problem is caused by packing libgtk. I guess libgtk2/3 are on the AppImage/excludedeblist for exactly this reason. Simply delete usr/lib/libgtk* can solve the problem. You may also want to delete usr/lib/libgdk* to get rid of that pixbuf warning as well.