We added really basic support for exclusion zones in v1.1.0. It simply discards tiles that are inside a rectangle, so it can exclude quite a large area when you’re zoomed out. But if that works for you, you can find the option under the “Experimental” section of the Tileset properties:
We plan to ship a more robust version of this in the future, but don’t have a definite timeframe for it yet.
Kevin