1) The type of apps that worked earlier (namely the while loop WAITMENU call) such as emptriv will continue to still work. Basically the things that can be done with WAITMENU have just been extended to do things like be able to change menus within an app and have apps be able to smoothly start and close themselves. So, yes, everything should be backwards compatible.

2) I'll leave this to Mark, I have no clue.

BTW, Mark deserves all the credit for implementing this stuff, I just tested it. Hopefully my contributions will be released in a few days. (Namely, job control for userland apps and another app I just started on.)