[ ] Version requirement needs to be dropped to match Moodle 3.3.9 minimum version
[ ] Adding a subblock needs to not rely on the parent block for default region for some reason, but should query the block manager for default region (may affect Moodle if themes declare different regions for different layouts)
[ ] Breadcrumb trail is wrong in Totara for some reason; adding a multiblock seems to target a completely different course
[ ] The base block_edit_form class declares definition as final so that might make the proxy form different now (perhaps a definition_after_data to strip everything out, hopefully it won't need nasty monkey-patching via reflection and eval)
[ ] The manage multiblock screen has a broken image in place of the i/empty placeholders
Would be nice if it could work on Totara 12+