The reason to avoid creating VMs BEFORE doing a planned system upgrade to a new distro, is because the qemu-virtual-machine used will be for the older release. For Linux distros, changing the motherboard model to a newer one isn't an issue that I've had, but for some commercial OSes, like that "other OS", you'll be stuck with the old fake motherboard, perhaps for decades, since changing the motherboard will invalidate the license. For example:
Code:
Win7Ult.xml: <type arch='x86_64' machine='pc-i440fx-trusty'>hvm</type>
WinXPPro.xml: <type arch='x86_64' machine='pc-i440fx-xenial'>hvm</type>
If I change those, bad things happen, like license reactivation is mandated.
So, when USB5 becomes available and your OS was installed with USB2/3 as the only known options, then the newer hardware won't support the faster connectivity.
Just something to consider.