Theoretically you could yes, however theres some things to keep in mind. Firstly USB is going to be slower than SATA, thats obvious. Secondly thumb drives are made with cheaper memory than an SSD, and have far less write cycles. So if you plan on using them heavily they will wear and start to error out eventually. This could take a year, could be more, could even be less. Just something to keep in mind. Its not a bad idea for experimentation, but in practice can be clunky and unreliable. As Someone Somewhere suggested truly running multiple OS's properly on a machine is going to need VM software and proper configuration.