First of all, I am not a Pentax fanboy. I have never been a fanboy of anything I use and I have never called myself a Pentaxian although using it since Z1. I was thinking about moving to Sony Mirror-less full-frame a while ago and asked myself a similar question. I sold most of my lenses and ready to jump the ship late last year, but the more I look into A7's family the more I feel like I shouldn't go there. So I still keep my option open.
Here are 4 most important things for me:
Dynamic range: Pentax use Sony sensor, so it is not much to debate here. I like what Sony is doing on their sensor technology and thank them develop the technology for another brand to use as well. But sometimes I am surprised at how far they push their own tech on their camera too. The Pixelshift video posted by @jgnfld is a good example.
Lense prices: To me, the lenses I will likely buy if I move to Sony are way way too expensive for a hobbyist. Note that I want Autofocus lenses. As I live in Japan; it is a lot more for me to select both new & used, digital era & film era on Pentax's land. You better look into the list of lenses you want too. A lot of my Sony friend have only 1 or 2 native lenses and they look at my (used to have) collection with envy eyes, lol.
Weather seal: No, I am not always shooting in the rain ... but I like to shoot in the rain and do it often. I have been using the K3 during typhoon days. Rain and wind are a lot worse than in this video
Typhoon type of rain is not a problem with the K3 so I expect K1 to be as good or even better.
Size and weight: This is a debatable area for me. Weight and size when talking about body + lenses, Sony is still a winner to me but not much because K1 body might be heavier but I don't have a taste for larger heavier lenses anyway. So again, It is a lot of good older Pentax autofocus lenses in the market. I can save myself a lot of Grams and $$$ using those options. (Yes, I like good lenses and I know about the modern lenses' design for digital sensor arguments but I couldn't care less about the few pixel on the 4 corners of the image.)
I am still using K3 and looking for an alternative lighter FF body that's why I have an idea of moving to A7 options in the first place and found out things I mention above after really look into it. A kind of coming back to a full circle! (And Yes, CP+ early 2019 was just another disappointment for me which I am a kind of sick and tired of it.)
Anyway, ask yourself what matter for you most and what brand has the better solutions. You might come up with a different answer than me.