Multiple versions of a plan

[thefotios]

It would be really nice to be able to "update" a plan and query and be able to see all revisions from the same URL. It would be even better if you could do things like show 2 plans side by side or show diffs in the query.

I could see this being useful when trying to optimize a query where you could see old versions and how things change. It could also be useful as a teaching tool. Sometimes I'll create before and after plans with teammates to help show what some optimizations can do to slow queries.