I would recommend a snooze feature on text messages where I would receive a reminder at a certain time to look at the message again. This would be like GMail's snooze feature.

Also, I would like to be able to flag a message / conversation to remind me if I have not heard back. Again, Gmail has this feature where after a few days it reminds you to follow up. However, it would be nice to pick from a few timeframe options from an hour or two, up to a few days.

With many people communicating via text instead of email, I think these features would really improve the app and usability.