We’ve definitely heard from a number of folks that they want JSM support on Forge and it sounds like we’re investigating how to get it done:
My thinking on this (and I’m very specifically saying this is my thinking on it, others may chime in with other ideas) is that the idea is to build an app that works on Jira Software as though it were JSM. I think about an issue as a unit of work, regardless of which tool its in: Trello, JSM, Jira Software, etc. You may be able to run an IT project from any of these tools (though yes, JSM is definitely tailored to this use-case). So an app that helps enable the running of that type of project can be built for any of them.
In some future world, a Forge app may actually be able to be run across all of the Atlassian products! It would be cool if the notion of a unit of work were abstract enough that you could build a single solution that worked across JSM, Jira Software, and Trello.