It would great to have sandboxes such as "reports" and "i18n" back as well as a place for devs who can't publicly host MBS(/BB/CB/…) instances to have a place to work on and showcase code they're working on.

Maybe it can be more containerified than it was before, so everyone gets an entire system to play with (but only one outward facing port?), but any way, getting sandboxes back would be appreciated.