Belt Driven, Hub Geared, Rack Mountable Nippy Commuter - Frameset?

Main problem with the Genesis is track-ends + disc brakes (and potentially mudguards).

You need to loosen off the rear brake caliper in order to slider the wheel forward and remove the belt/chain.

Rear wheel changes would already be fiddly though, as you also need to disconnect a cable from the Alfine too.

Use sks mudguards and use the mounts intended for the front wheel at the back. The guard can then be popped out giving room for the wheel to move backwards and out of the drop outs. I've never had to touch the brake caliper to remove the rear wheel. I've also found it unnecessary to disconnect the gear cable to change an inner tube... Bike upside down, then remover the wheel and lay it flat across the underside of the chain stays with the gear cable side of the hub facing the floor.

The Genesis 853 frames are great... Go for it!