Thank you all for great responses!
As for two bodies - I've done several times multi-day treks for which I have a big backpack (15-30kg) on my back and a big top-loading case strapped to my chest. I know from experience that if I put there one body and an extra lens, I will almost never use the other lens, because it is impractical for me to change the lens while hiking. Most of my shots are taken with the backpack still on my back, as my travels are never photography expedition, so time is limited. Therefore I stay with two bodies, accepting the weight implication. That doesn't mean I wont to drag another few kg of lenses though

I thought earlier or going one body + ultrazoom, but the compromise on quality was for me too much. I also used to have Sigma 105/2.8 Macro and the distance was not really for me. As I say, even with the 50-135, vast majority of keepers are for me either landscape/portrait on the wide end, or close-up on the long-end.
I've been looking through the forum and elsewhere already for some time, so perhaps information overload caused that I missed the bit that the PLM version improves also the optics significantly compared to older versions. The autofocus improvement would not convince me to go for PLM, but improved IQ probably will. The point that I actually take most of my shots during the day is also speaking for 55-300. I could have the 55-300 on K-70 and strap the 15 Limited to K20D, with option of upgrading the second body later to one with PLM support. Has anyone compared the FOV on the wide-end (ideally with 50-135)? Do you think I will notice the difference 50 vs 55mm?
The Pentax HD TC is quite expensive (almost like the 55-300

). I understand it's a quality piece of equipment, everything works natively and it's also quite light. But I am thinking whether I want to spend 400EUR on something that I will probably use only occasionally and does not add THAT much range. I was thinking about the Pentax 1.7X, which can go second hand for 200EUR and perhaps help with screwdrive when SDM dies one more time

But I guess it doesn't pair that well. Alternatively a cheaper Kenko 1.4X, which could lead to no AF then (I could live with that). 2X would be something I would appreciate in terms of range, but I read/saw mostly negative results. Do you have experience with the 1.7X or cheaper 1.4X on 50-135? It is my understanding that differences can be significant model to model. Or have I missed something?
It seems the 60-250 is not so recommended here and indeed it is also not my favourite. Noone really also went with the 100-300 option, I guess mostly because the 55-300 PLM is a light and compelling option. So I guess I the choice is really narrowed down in my mind to 55-300 PLM or 50-135+TC.