Enable the ability to flag a conversation upon sending a text that watches that conversation for a reply and/or snooze the conversation.
Several options could exist. It could watch for a reply and if no one texted again for your predefined period of time, you would get a notice in Textra. Or you could just tell Textra to remind you about the conversation regardless after a set period of time.

I use Boomerang for Gmail and Gmail's snooze feature quite a bit for business. Many people rely on texting for communication as well and to have similar features would be nice. I think this all can be handled on the app side.