Linux apps generally expect a full software stack. Android's userspace is radically different (and for good reason). There's no GNU libc or GNU coreutils or GTK/Qt or X. There's a minimal libc implementation, busybox, and an Android-specific framebuffer-based GUI framework. From the source it appears that Google have tried hard to exclude GPL'd code as much as possible, too.

Getting Linux apps to (natively) run on Android isn't really affected by this news. The kernel was already as close as it needed to be. It's userspace that's the issue.

You can recompile most Linux apps to work on an Android phone now. Anything requiring graphics will require a complete rework, though, because Android doesn't have X.

Linux apps already do work with android.

Just be rooted and get this: http://android.galoula.com/en/LinuxInstall/

No. All this means is that the delta will be lower, and new kernel work will be able to cross-polinate a bit more easily. Though manufacturers don't really follow the mainline's upgrade path, and it seems like they will converge on this (embedded LTSI) instead: https://lwn.net/Articles/484337/

Afaik this means the converse. This will help run Android apps on vanilla Linux systems (eg desktops). Note that kernel is only one piece of the puzzle, but with these patches porting userland should be easier.