@Bolly
For Ubuntu Touch this bug isn't critical because device is designed for single user and local access is standardly full.
I have looked at this part of the Q/A and the only reply addressing the real issue (confined apps) is not mentioned in the written report. It was done by Marius Gripsgard (amid a lot of verbose disgressions about servers) and basically it was that apps are open source and that apparmor is applying so it's all protected.
re: open source: it's not true that confined apps can't be closed source.
the policy states 'Only open source applications allowed for manual review: '. That means that confined apps are not necessarily open source.
Anyway even with open source apps, it's not a sure thing that first, the source will be looked at and that the review will catch everything - hackers can be crafty and it's pretty much something they must be if they want to be in the business-, and second, that the binary uploaded to the store matches the published source. As far as I know the apps are not compiled by the store.
re: apparmor: yes it protects some, but I doubt that apparmor is able to stop all kernel vulnerabilites because apparmor is part of the kernel, it's not a supervisor above the kernel.