I own a K-3 but it's getting on. If it were to fail today I'd be looking looking at the K-P.
Reasons...
The accelerator chip... )also in the K-70.) Same low ISO performance as my K-1.
Pixel shift. I love this feature for macros.
Tilting back screen. ( It's great, especially for macros of mushrooms etc.)
Most recent AF algorithms, apparently noticeably better than the K-3s.
IBIS works with all my old lenses.
My daughter in law still has my K-x and still makes good use of it. But, it's not like my K-3 in any way but taking the same lenses.
To my mind, the K-P and 21 are made for each other.
But you won't go wrong with a K-70 either.
Pixel shift...
There's no stationary lighting condition too tough for this feature..
On the K-1
The flip screen for macros, once you've done it you won't know how you survived without it. Also Pixel shifted.
The increased ISO performance will give you a stop faster shutter speed for freezing the action.
That in itself could be a much bigger deal for street photography than you might imagine. Personally I'm often in situations where an extra stop of high ISO performance would have made possible many images I missed.