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.