wizdum:
I thought SATA was hotplug-able? If not......oops.
I didn't know that, but it seems you're right - it is hot pluggable. However, that assumes you're using standard SATA connectors to make/break the connections, and also that you're powering the device via the SATA connection. If you're going to physically intercept the wires then you would need to determine the correct connection/disconnection sequence and ensure that your switch/relay system followed it.
This strikes me as a lot more dodgy than the original solution of powering the drives separately and connecting them via a standard USB hub - I am simply not convinced this is going to be a more reliable solution.