I actually have access to a spare 2413U from my brother-in-law, so my plan was to keep both running, (if I can adapt to the 2413U) register all the devices on ISY and migrate several events at a time. A cursory look at my HS shows about 25 Insteon devices registered, and about 20 X-10 addresses in use. Of course, and one of the reasons I've been reluctant to switch is I also have dozens of virtual X-10 addresses being used by some of Jon's HS plug-ins. Frankly, his plug-ins give more function to HS than the app itself, but I digress. I'll have to find another way to fill that void.
I did use a serial to USB adapter for my RCS RS485 thermostats with HS, and that worked flawlessly for years. They aren't that expensive. I may just roll the dice and try it.