What Greg is saying here is correct. There are a LOT of limitations to preemptive threads which is why applications tend to use processes these days instead which is exactly what you get when you use the Worker class. Large parts of macOS, Windows and Linux are not thread-safe. We could quite easily make preemptive threads available but then your apps would start crashing every time you accessed something that you didn’t realize was not thread-safe. If we spent the time to go through the framework to make sure you’d get an exception if you tried to use parts that were not thread-safe (a project that we believe would be measured in years not months), there wouldn’t be a lot left.
Having said that, if you have situations where preemptive threads are the only solution, please comment on the issue so we have that all in one place. Ultimately we want you to be successful and in some cases we may be able to help with a solution you can implement now. Also, if there are features you’d like to see added to the Worker class, make sure you make feature requests for them of course.