[Suhail]

Okay, I did just such an upgrade, despite the fact that I (at 78) thought I had just bought my "camera for life" camera when I bought the KP. (Which, by the way, I loved, especially with the larger handgrip and battery grip).

So why?

Well, yes - as you have noted, like probably many others, I (being first a bird photographer) wanted better BIF shots (And I like to think I have got them!)
I love the little joystick for easy moving around of the focal point within the frame - great for ensuring you get ALL the bird in the frame when shooting larger birds close-up.
i believe the autofocus is better (especially in low light), and I think (am I deluding myself?) that I get more shake reduction assist on the K3 III when shooting with "the MONSTER" (the 150-450mm zoom!) hand-held.
The on-top LCD screen gets a look at, sometimes!!!
The standard grip (without battery grip) on the K3 III is great!
Better battery life without needing a battery grip on the K3 III.
I probably don't use the fastest burst mode much, but I do use medium burst on the K3 III (again, mostly when "BIF-fing").

Have I noticed the much-touted better view-finder experience? To be honest, I am not sure I have. (But then, maybe my 78 year old eyes are to blame there?)
I have been prepared to chance higher-ISO shots (to maintain higher shutter speeds when hand-holding the Monster, but would be dishonest if I said I have done a fair comparison on comparative high ISO performance between the KP and the K3 III.

On long day outings, I take the KP along as a second camera (the Monster on the K3 III, and either the 100mm Macro or the 16-85mm zoom on the KP) but to be honest, the poor old KP has spent a large amount of time staying neglected in my backpack most of the time since I bought the K3 III. (Although the KP's pull-out screen does come in handy for shooting low-lying mushrooms and the like!)

I am not a "technical" photographer - which is to say I am probably guilty of not even having an awareness of many of the K3 III's many "in depth, hidden features" - but that would probably also be true of my use of the KP before I bought the K3 III.
Which is not to say I would not jump at the chance of spending a day of learning with an "expert" on all the technical aids and wonders hidden inside the K3 III !!! Even though I most probably wouldn't even know which questions I need to ask!!!

I will be fascinated to see what replies you get from others. Hopefully, the replies of others might bring to light many of the "hidden" goodies I would use if only my technical savvy was more up to scratch!

So, I think you have might have started an interesting thread!

PS - this thread may become more enlightening for everyone if you revealed your own "intended uses".

Informative post!

I believe what you provided will be my reasons to buy Pentax K-3iii too.

[cport]

In which case, assuming no alternative body becomes available in the meantime, the K-70/KF (or whatever it might be called when your KP finally does expire) might be perfectly suitable … very similar image quality, and fully articulated rear screen, just not quite the low light performance. Mine still has it's place in the scheme of things

No way! KF is not a replacement of KP. I would not get back because it misses many KP features. I will likely prefer an older KP (or KP II), or I will get into K-1 II or K-3 III.