Will imports always be necessary when pattern matching on sealed types, or could there be something like the provision for enum switches?
We could expose a model where a sealed nest is more like an enum, and the nest members are more like enum constants, in which case using the same rules as for enums would make sense. If we thought that was the right model for sealing. If we end up not relaxing the rules regarding aux classes, we should consider this for switches (but it doesn't really address the more general API design question.)
It is true that in many other languages, sealed types are mostly intended for "sums of products", which is a reasonable 80/20 target. Though I'd rather see a deeper / more orthogonal treatment (though that does force us to work through more details.)
The hardest downside to the proposal
There's not a proposal, yet... There's just a discussion, proximately motivated by an external comment, but one that has been on the drawing board for a while, since we started to look at more concise ways to express sum and product types.
