The term "LSM stacking" is public. Search for it and you'll get good material.
> Are you going to convince Red Hat to
That's not how things work. Canonical and RedHat collaborate technically by improving parts of the system as necessary. Things are enabled or not based on market requirements.
> What about helping to maintain AppArmor support in Fedora?
Canonical already does that by working to upstream the patches. That helps Fedora and everybody else too.
> I'm pretty sure that everyone will say no to the idea of combining AppArmor with SELinux
Well, no need to guess.. there are open discussions about it.
> I think you missed the point. But sure, maybe. If there wasn't the CLA to get in the way...
For legal reasons that are not unique to Canonical we do require a pretty straightforward CLA to be signed. I've signed that sort of CLA myself for other large companies, both individually and in the name of Canonical, so the playing field is level here.