I'm sure there are reasons the implementation might not be easy, but conceptually this seems fixable. You just need a lower bound of "how bad can this plan be?" and that doesn't require completing the query, just observing that it's been running for a long time and/or used unreasonable amounts of resources.

Also, is the problem with the 50 join query that the planner screws it up, or that it's fundamentally doing too much?