Re: rear or front mounted engine kits not for me
I have to wonder if your opinions/assumptions are based on experience. I've had the opportunity to ride a number of rear rack mount bikes, both with the engine centered over the rear wheel and mounted side saddle, off to the left. I'm a lightweight, so if the weight or balance were factors I would have surely felt it. I've never experienced any instability or balance problems with either application.
That being said I will admit that, like you, I prefer the looks of an in-frame mounted engine as well as the ease of mounting/dismounting the bike. Rear rack mounts require that you either step very high, swinging your leg up and over the engine, or step across the top tube. A girl's bike (step through frame) would lend itself better to the rear mount, me thinks.
As for a front mount; I've never owned or ridden one so I will withhold any opinions on them.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"