I assume you're aware of the S5 II? Should be a little smaller than se S1, I've gathered. No OVF, though, thus no cake...
The Panasonic S5ii is a great idea, to replace S1. I initially dismissed it on three points: (a) the EVF is not as gloriously specced as the S1, and (b) fully articulating screen, and (c) high price, since it's fresh new.
But I then noticed a deal for a brand-new S5 kit. Get the S5 and 20-60 for 1800 €, get a 50mm f/1.8 thrown in for free. The body will cost about 1100 € after lenses. Can't get the same kit from MPB for example.
It's getting my juices flow a little bit.
For point (a), but of course S5 has even lower-specced EVF. Oh no! But I started to reason: I'm happy focusing manually with Olympus E-M1.2 and it has the same specs but I think Panasonic is feeding the EVF better signal, making it better. So maybe (a) won't be that bad.
For point (b), I can tolerate the FAS. With manual focus lenses in the dark one "cannot" use the screen anyway to much good. Back-screen-composing is an affair with autofocusing native lenses to me.
I haven't held an S5 in my hand but I can trust it to be a good one, ergonomically. G9 and S1 have the goods. Panasonic DNA is fantastic. I would miss the top LCD, though.
But perhaps overall, going this direction is not the best idea. I want to be losing, not gaining. And it's 1800 € which suddenly feels like a lot of money.
It also seems like your Fuji itch isn't going to go away without scratching. Just keep in mind the X-Pro OVF is of limited use. I'm not sure about the later versions, but on the X-Pro1 it was only useful for a couple of focal lengths, having only two magnifications.
I was researching this aspect the other day but I think I got lost.
But if I understood correctly, the framelines adjust to arbitrary FLs which is better than on M. There are two levels of magnification, which is one level more than on M. Sure enough, both levels are inadequate for tele lenses such as 90mm/135mmeqv? Should see it firsthand.
Review: Fujifilm X-Pro 2 - Page 2 of 4 - Admiring Light this page in this review gives me an encouraging writeup what to expect. I know rangefinders so I don't certainly expect it to be usable with 200 mm lenses. Simple optical realities dictate this.
But since you already have the Leica, what good would you get from the X-Pro?
This is a mighty good question.
I have adapted Nikkors on my Leica M and it can be a pleasant affair where I focus using the EVF and then shift my eye on the optical rangefinder to time my shot.
But the EVF on M is not very good. The optics in it hurt my eye, it's a
huge battery drain, the resolution indecent, and night sight nonexistent.
Fuji X-Pro2 gains two alternative EVFs and an easy switch to flip between EVF/OVF. I've used the X100 to good success and appreciate the implementation of the switch. People say the corner EVF causes some inexplicable lag, which is my main concern.
Then the X-Pro2 also gains a couple of stops of ISO performance over M, even if the sensor mosaic and noise pattern can be a hit/miss compared to M. Burst speeds also help.
And a select few native Fuji lenses interests me. It can lead to a bad path, to an unhappy place.