You still need to maintain that sandbox. Ultimately no one wants to spend energy maintaining software that isn't used very heavily. That's why feature depreciation happens. If someone cares enough, they should step in an offer to take over long term maintenance and fix the problems. Ideally a group of people, and perhaps more ideally, a group with some financial backing (eg a company), otherwise it may be difficult to actually trust that they will live up to the commitment.
Even projects like Linux deprecate old underused features all the time. At least the Internet has real metrics about API usage which allows for making informed decisions. Folks describing how they are part of that small fraction of users doesn't really change the data. What's also interesting is that a very similar group of people seem to lament about how it's impossible to write a new browser these days because there are too many features to support.
"The sandbox" in this case is their ability to execute WASM securely. It's a necessary part of the "modern" web. If they were planning on also nuking WASM from orbit because it couldn't be made secure, this would be another topic entirely. There's nothing they're maintaining just-for-xslt-1.0-support beyond a simple build of libxslt to WASM, a copy block in their build code, and a line in a JSON list to load WASM provided built-ins (which they would want anyway for other code).
The word is "deprecation", and your understanding of what it means isn't how it has tended to work at all. The Web is not the Tizen SDK. This is a significant change to how browser vendors treat Web standards.
Even projects like Linux deprecate old underused features all the time. At least the Internet has real metrics about API usage which allows for making informed decisions. Folks describing how they are part of that small fraction of users doesn't really change the data. What's also interesting is that a very similar group of people seem to lament about how it's impossible to write a new browser these days because there are too many features to support.