For people who don't use root apps this is actually good news. Strict SELinux policies are going to help boost Android security significantly. Malware devs are having a field day on Android and root access only makes it easier for them.
Bullshit. The massive holes in Android security are caused by the inept app permissions system. Restricting hackers that jump through hoops to get access to their file system even more is not going to stop the thousands of apps that spam all your contacts, etc.
Rootkits can cause way more damage than permission abuse. Spamming your contacts is nothing compared to keylogging your bank information or snatching 2FA notifications. App permissions also need to be improved but the former is higher priority IMO. ACL has existed in computer systems forever for a good reason. It's pointless if its not properly enforced via MAC.
Now they're adding a slew of SELinux policies which also enforce read-only access to /system partition. These are still applied if you remount it rw, which means that in the future users will have to modify SELinux policy to write while the OS is running.
Recovery (which is tasked with updates) will keep its write ability. Also all apps which don't write to /system partition (which includes most root apps like Titanium, etc.) will not be affected.