Apparently Samsung have dropped sales and marketing of digital cameras and camcorders in the UK due to a fall in demand
https://www.amateurphotographer.co.uk/latest/photo-news/samsung-to-axe-digital-c...
So presumably not even Samsung sell the NX series now, and if Pentax had badged them, they wouldn't be now.
According to Ama zon, a not even in stock NX1 retails for £2400, much dearer than a K-1. I know which I prefer and SRS still sell them! And surely a FF sensor is better for normal digital photography?

They all come back eventually!

https://www.ebay.co.uk/itm/Vivitar-TX-Mount-Adapter-Pentax-ES-Mount-Boxed/163145...

Any good?

Would that involve butchery? If so why not get a K-1 and use it as intended as is?

The CIPA rated battery life for the K-3ii is 720 shots.
https://www.imaging-resource.com/PRODS/pentax-k3-ii/pentax-k3-iiA6.HTM
however, that would include using the flash for some of them too. So achieving up to 1000 before it fails seems to be par for the course.
What is the battery charge indicator showing when the failures start to occur?

Given the huge number of shots before it fails, it does sound like a weak battery in the K3ii.
Have you got a spare you can swap over with when the issue occurs? If that solves it it'll confirm the problem. If not it would surely be the camera itself, but it's odd it'll take hundreds of shots in a session and then fail, yet be OK again next time. I'm guessing you'd have charged the battery in between sessions?

Edit: One thought that comes to mind is if the camera is getting hot in an extended session and that is somehow causing a problem A capacitor failing perhaps causing it to run hot?

I use one of these:
f:0" rel="nofollow" class="outlink" target="blank">https://www.ebay.com/itm/JJC-ALC-MX1-Auto-Open-Close-Self-Retaining-Lens-Cap-for...
Saves the lens mechanism trying to force it off.

Just to add I stuck with the ME/MX/K2 until the digital era as to me their successors seemed plasticky and inferior (starting with the A series.) At least that argument can't be levelled at the current crop of Pentax's which are indeed quite resilient and to be fair, less bulky than some of the comparable opposition.
It's all very well having a set of the wonderful new Pentax lenses (as indeed they are) but if because of their weight they would get left at home some may think twice about purchasing said items.
Someone enters a camera store and compares systems today, they'll find the current selection of K lenses are very heavy. Some may not worry but quite a number will. Pentax need to look back at that ad from the 70s which got them to the forefront at the time. They've shown they can do it for APS-C, they need to look at 135 format offerings too.
A lens that fits in the gadget bag is more use than one which doesn't, however good it might be, and the answer isn't necessarily buying a larger bag!

The fact it's better is certainly not in dispute. But for a focal length I haven't historically used regularly it's a lot of money unless it can replace several other lenses, mainly wider so it can't really.
I used to carry a 50 for the wider aperture when using 25 & 64 ASA slide films but there really is no need with digital.
If I was regularly photographing in night clubs and theatres etc. it would make an excellent choice.... but I don't! So for the few odd occasions when I need a 50 1.4 I'm happy to get by with what I have. Now if a bargain was to come my way may well buy it to add to the collection. But would I use it or leave it at home? Who knows! I think I'd be more likely stick the smaller, lighter FA in the bag for a just in case I want to use it lens.
As you have said, the 43 is a better lens than the old 50 and I prefer the focal length so I'd be more likely to take that as indeed I regularly do. In the past I was a fan of the 40 pancake and a new one of those would be high on my list to buy. Not sure why they brought out several for APS-C though. Shame the limited one wasn't fully FF as the design of it is pretty close to the M version, but with smaller elements.
I got into Pentax more when with the K mount it became the smallest and lightest SLR system on the market at the time.


The recent lenses seem to have gone in the opposite direction and maybe this is adding to the defection to M4/3rds systems. Most people don't wish to lug heavy gadget bags any more.
I don't believe the old lenses are performing any worse than they did in the past just because something new has come along!

Something you don't see every day. Well done to the Mrs.