Yeah, the K-S1 seems really cool, but try getting one of the newer models like K-70 or even KP. These should allow you to use PLM lenses and give you.. slightly better video functionality.
I looked into m43 and Oly some months ago, but it didn't make economical sense. Those cameras are not cheap, and their lenses are even more expensive (and can be quite big, as well)
So if you have a decent set of lenses, stick to Pentax K.
If you want to do video, then think of switching to Sony or Canon. Better yet, get a camcorder.
I don't do much video and my old Pentax cameras are good enough for what little I do. And I've even seen some stunningly good video taken with Pentax DSLRs. Check the video subforum - skills, lights, planning, video rigs are really important.
---------- Post added 30th Jun 2017 at 02:07 ----------
Originally posted by lapeen really tempting as it's reasonably priced and seems to do everything I want it to do. Any thoughts?
Temptation is everywhere. Make a list of your priorities, then check which cameras/systems can meet them, and count up the cost of switching to that system.
Edit: Also, go to a store and handhold the cameras you are interested in. To me, the lower and Canikon feels pretty terrible; not as sturdy and intuitive as Pentax cameras