I think Missouri is more likely, because I think the electorate there is more flexible than the electorate in Kansas. I think Trumpism has caused many people to think that the rural areas of MO have permanently shifted to the GOP by huge margins. But I think Trumpism is not going to last for much longer, and when many rural voters have gotten Trump out of their system, they may revert to some of their ancestral moderate Democratic tendencies.
Other than a hunch, what makes you think that? If anything, I think these areas could become even more Republican. Aside from a dead cat bounce leftward or a heavily negative environment against an incumbent Republican like W, I don't see these areas moving leftward anytime soon.
To add on to this, MO rurals represent a significantly higher share o9f the state's population than KS rurals. A lot of R votes in KS still come out of major cities like Witicha and Johnson COunty. I'd argue these voters would be more flexible if anything.