I would like to know about Heroku's HTTP/2 support.
HTTP/2 is not currently supported on Heroku although this may change in future. You can find out about our currently supported HTTP protocols here: https://devcenter.heroku.com/articles/http-routing#http-versions-supported
For any future developments we recommend subscribing to the Heroku Changelog. This will let you know about updates, improvements and deprecations ahead of time so that you can make any necessary adjustments.