Thing is, shifting the multi-speed options (dérailleur or internal geared hub) does absolutely NOTHING as far as a friction drive is concerned. A friction drive has only one ratio - drive spindle/outer tire circumference. That's all it can provide, except for slippage. Like a child's tricycle, an FD system is direct drive - no effective gear choices.
Now, it is quite possible to build an FD system that would be capable of at least two, and possibly more speed ratios, and "shift in motion". It isn't even all that complicated to do.
As far as the durability of most internally geared hubs goes, think about what they are designed to do. To wit: stand up under the torque load of an adult human being standing on the pedals, pulling on the handlebars and bearing down - a much greater amount of torque than most any small engine will ever produce.
The biggest problem is transmitted vibration and the design of all but the NuVinci hub - they all use internal cogs. The greater the number of gears provided, the thinner those internal cogs tend to be in construction, and the more susceptible they become to vibratory failure.
So, using good motor mounts that lessen vibration transmission, and the SBP jackshaft system (which further isolates engine vibration from the rear hub just by its design) should not cause undue problems.