You bring up some good points. I could use something like GChat, although idk if that works with my school's GSuite setup. That being said, I've tried spinning up chat apps like Slack/Rocket/etc. and faced serious issues.

A. Nobody checks Slack. In the beginning everything's great and people are engaging on slack, but after a few weeks engagement drops off.

B. The number of people without Facebook has been precisely 1. If there were more people without FB accounts, I'd 100% consider another option.

C. Begrudging use is better than no use. It's not that students are boycotting my program because they have some hatred of Slack. It's more that they're confronted with a form, which they put off and then forget to do.