A lot of tests are sharing one resource (USB device) which can't be accessed in parallel. So that's my constraint which I need to live with and the main reason

A lot of tests are sharing one resource (USB device) which can't be accessed in parallel. So that's my constraint which I need to live with and the main reason why I can't parallelize or offload testing to cloud. Otherwise yes, you can run tests in parallel in vstest. That's completely possible.