I get the perfectly concentric bit; think it was Rotel that centred around the bb back in the day, although more exaggerated with a large chainring. I don’t really understand the packaging bit.
Basically if you don't want to use the offset output shaft as a pivot there's very little room to attach a pivot for the suspension that fits between the gearbox and rear wheel & doesn't foul the chain. With high-pivot designs becoming more prevalent it'd be more practical/accepted these days, but still presents a fairly small window of pivot placement and would inhibit shock placement (Horst link/four bar with upright shock) or physically prevent it altogether (anything with a shock through the downtube like lower-link VPP, Forbidden, Deviate, etc...) like on a lot of the current common suspension designs. It still allows room for a shock that attaches to the top tube, but it's a bastard (in my limited/hobbiest experience) to get a decent leverage curve out of those designs (assuming you want a nice steady rate of progression in the linkage).
If you want to nerd out with it download Linkage V3 and have a play. It's quite interesting how difficult it is to design a system that would both work well across all performance factors (leverage ratios, linkage progression, anti-squat, anti-rise, pedal kickback, chain growth, CoG dynamics, etc...)
and not create any physical clashes between chainring, chain, chainstays, wheel and tyre, and tyre and seattube. It's good fun if you like annoying your brain with nearly impossible problems...
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)