I would love a modern version of the N900/N810. If I could get one with a recent ARM processor, good slide out keyboard, and running a more desktop-oriented Linux install (meaning more hacking/developer friendly than just Android), I'd be seriously tempted. Sadly, I assume the current component prices would mean it would be too expensive to be realistic.
The FxTec Pro 1 is the closest I've found these days; it has a slied-out keyboard and an unlocked bootloader so you can run LineageOS or Ubuntu Touch (PMOS support seems spotty).
The keyboard isn't as nice as those on phones from ~2010; it's a bit too big for the thumbs to really fly and sliding it in & out is not as effortless as it should be, but nless you count Unihertz's blackberry-likes, there's really nothing else around that comes close!
Funny I was a supporter of their devices I bought both phones, laptop, tablets... Issue is the software man no drivers. Like the e-ink tablet had a great design/screen but the brush stroke was ass would leave dotted lines as you drew then it would render solid on lift up.
I'm complaining even though I'm not writing the drivers myself I get that.