That said, the open source version provides more than Monit in a better, easier to deploy package. I think that right there is incentive enough to use it. Plus, if you want to fork it and add your own specific notification channels, here's the source:
https://github.com/mperham/inspeqtor/blob/891517cc0edc6dda8d...
Just because mperham wants the project to be sustainable doesn't guarantee it. However, if sidekiq Pro would have failed, Sidekiq would easily survive simply because of huge open source community. With inspeqtor it's not so clear.
"Route alerts to your team chat room" is listed as a Pro feature. Any PR implementing it is unlikely to be merge in. And creating a separate fork for a relatively small feature should not really be an answer to an open-source project.
The OSS product is targeted to small teams, individuals and hobbyists. Pro was designed to target larger teams and the features they would need.