The kind of folks running TextSecure have already made an effort to install a replacement messaging application, hopefully this helps them also pay attention to the warning.

If nothing else it'll slightly slow down a worm utilising this exploit...

It mitigates the worst part of the threat: An exploit that happens without any user involvement.

First of all, TextSecure does display pictures in MMS. It just doesn't call out to stagefright to do so. I've never recieved a video message, so don't know how that works.

Second of all, the difference between a 0-click infection and a 1-click infection is huge in terms of time it takes for a worm to spread.