I think there are probably a miniscule fraction of 1% of ppl still using a USB mouse. Even most of those who still need a mouse (I don't see a valid use scenario beyond professional graphic design production) have a bluetooth enabled one.
I bet that children who are being born today probably won't understand why there was ever things such as usb thumb drives or wired mice, just as most of us today don't really understand the existence of floppy drives and ethernet jacks on laptops.
This "future state" is further away than you think....
I think you'll find that a lot of people still prefer to use a mouse instead of a trackpad - even an Apple one, which is the best in the business.
Looking around my office, where everyone has laptops (nearly all Windows machines), I'd say that over 90% have a mouse connected, and the majority of these are wired mice. If they were using Macs, I would expect this number to be lower, but the practice of using mice is very much alive! I use my rMBP 15 happily without a mouse, but if you need to do a significant amount of "precision" pointing or object manipulation, e.g. graphic design, video editing etc, a mouse is a lot easier to use than a trackpad.
I think nearly everyone on this forum will be familiar with floppy disks and certainly Ethernet and understand what they were / are used for. I will nearly always use Ethernet if it is available, because it is still a *lot* faster on local networks than any current wi-fi standard, particularly in a busy environment where bandwidth is shared. Even in my home network, wired Ethernet (1 Gigabit) is about 7-10 times faster than wi-fi for file transfers. I can't reliably play HD video to my WD media player over wi-fi (2 rooms away from the router), but wired Ethernet does this with ease.
I'm also pretty sure that external storage devices such as flash storage are going to be with us for a couple of decades yet - especially for mobile users who travel outside of large population centres in technologically advanced countries. I don't see true "global" wireless cloud connectivity (presumably provided by satellites) as being a reality for a long time.