Maybe CL got this right with the condition/restart system? In addition to their utility for experimental programming, conditions work really well for handling errors programatically.

The general problem seems to be something weird happening far down in the system, for which the correct way forward is dependent on how we got there. This situation can't be handled where the issue happened since that would break encapsulation, but unrolling the stack all the way up blows away the context that is necessary to understand how to move forward. I don't see how a system that either unwinds the stacks (throwing errors) or tries to encapsulate the state through the system (Either) would truly solve the issue.