More complete version management

[adriangb]

While there's a lot of things, I don't like about Alembic I do think they have a pretty solid data model for versions: https://alembic.sqlalchemy.org/en/latest/branches.html. It'd be really interesting to see what concepts we can pick up from them, maybe while still keeping migrations as edges not vertices.

[euri10]

topological sort ?

[adriangb]

Well a topological sort is probably needed somewhere. But really I think the interesting bits are around creating branches, the concept of HEAD revision, branch merging, having multiple "down" revisions, etc.