You seem to forget that the Platformers are slipping fast and the Kukiz in recent polls outstripped them.
We'll see how long he lasts when he comes up against an electoral machine that's used to winning elections. Kukiz won't only have to worry about PO, he'll also have to worry about PiS in the Eastern provinces. So far, he hasn't attracted any political power at all, which is what matters in an election. If you consider that Kukiz has a parallel with Twój Ruch in 2011, then look at how many experienced campaigners Palikot had to call on. Kukiz has nothing so far, and this will likely hurt him.
All these figures are highly speculative at this point, but just for the sake of analysis, let's assume that my prediciton is correct (65% for PiS/Kukiz). What in your view would be the result? BTW why should the major coalition partner give up the Interior Ministry. That is the main weapon against lawbreakers including PO-style white-collar crime -- juggling books, kickbacks, under the counter deals, fixed tenders, backroom payoffs, etc.
Disaster for PiS in your scenario. They would be facing a coalition partner that would offer them constitutional changes in exchange for some very odd populist policies, and it could lead to yet another 2006-2007 situation arising again. A better result would be something around 55% combined, as it would allow them to govern without the distraction of constitutional changes.
As for Kukiz, the MSW would probably be a red line in order to prevent Kaczyński repeating history and using the MSW against him. Remember, Kukiz is building his reputation on destroying the existing system, and allowing Kaczyński to control the MSW would be a disaster for him.
Looks like PiS are also realising that Kukiz is a threat to them.
rp.pl/artykul/1205747.html
To explain - MP Pawłowicz from PiS (of infamous eating in the Sejm fame) is mocking Kukiz for apparently having abandoned Poland already.
As for Duda, there are certainly growing murmurings that PiS may be starting to move away from Kaczyński's authority now that they've got someone to rally around. It's certainly telling that Duda won the Presidential election by putting in a lot of hard work, which Kaczyński has never done.