You mean something similar to this ?
So you can charge a backup battery while using the phone ?

I have bought a similar-looking device in the past. I'm very happy with this. It's also useful for camera batteries (the pogo-pins slide and can be adjusted to any battery +/- terminals).

Well, that would be good for quickly switching batteries, but also to access any other useful contact.
(Probably wireless charging pogopins, as discussed above. So people can slap a Qi charger. Or whatever else charging solution)

Personnally, I don't mind if this increases the thickness by a couple mm.
End-user replaceable battery is just too much useful.

In my case, it would be interesting to know if it fall-disconnects safely :-P
(I think the busted USB on my current Jolla comes from a couple of fall while connected to charger / or to computer)
It's a shame that USB consortium didn't go for a classic flat connector like Apple's Lightning (probably Apple managed to patent reversibility on such connectors).

I miss the indestructible connector on my first ever Palm IIIc....

Yup, I was indeed thinking to acquire some magnetic quicik-snap solution.