I was in the same situation a year ago, and this is what I remembered....
For the K7, it was released in mid May 09, and I purchased my K20 in April. Leading up to the K7, there was a lot of leaked information, building up anticipation, and then they announced a release date. Prior to that, the price on the K20 broke around Christmas a bit. Then after the first of the year, Pentax added on the 3 year warranty, then the price stepped down after it broke $1K, until it bottomed out at around $700 when the K7 was released. I bought knowing full well that the K7 was a month away, but at $700 the price was just too good to pass-up. Also, the exact features were just a speculation. I figured that the K7 would not reach the $700 mark for another 12 - 18 months, so getting the K20 made sense. Am I sorry for not waiting - not really. I have really enjoyed the K20, my skills have increased, and it was just what I needed at the time.
The KX, was somewhat of a surprise stealth announcement, as I remember. All of a sudden it was just there. No leaks, no build up, no real price break of the K2000/KM, leading up to the announcement. It is just me speculating that the KX was timed with the end of the K2000/KM production run and inventory depletion that reached a certain level.
The 645D again was also just an announcement. Pentax had made a number of references that it was coming, however they had said that for years. There was nothing to really replace, since the 645 film body was not in production, hence no prior model price reduction or warranty addition. No real run-up in announcement speculation like the K7. In fact there was some what of a run on the old film based 645 lenses that were available on ebay and KHR, on the day of the announcement.
So where does that leave the analysis. The K7 has come down in price, breaking the $1K barrier, currently somewhat wandering in the 900's. No real anticipation of a new body being worked up in the masses, with leaks. No real drops of information here and there. Pentax has not done anything really to even start to clear inventory - like the addition of the 3 year warranty. So, my guess - which is as good as yours, is that Pentax will announce something out of the blue, or it will show up at a one of the future camera shows. So, my speculation is that they will silently let K7 production end. Silently start beta testing, then start new production, while letting the K7 inventory deplete naturally. Then announce something new, when they have the new camera setup and ready to go. If you remember the K7's firmware appeared to have some pre-production loads for the first set of units, with a firmware update soon after release. Also, I remember that there were some beta testers that were publicly talking about the camera and images were posted. This did not happen with the KX.....
You certainly know that the new camera will be price above the K7's current price, and in this economy I do not think that you will see any aggressive price reductions to clear the shelves. I also think that the K20's price floor at $700 or so, shows to some degree the amount of price elasticity or softness there could be. So right now, I would guess that your playing with about a $200 or about a 20% margin. I can only guess that if they intend to come out with a new model, this year, that they would need it out and available for Christmas. So looking back to the KX again - which was out for last Christmas, it was announced in September (searching back on the web). So if Pentax intends to do something this year, it will probably be within the next 6 months and your probably risking at most $200 in price.
I was just reading in another thread that a retailer is offering the K7 and a kit lens for 899, so with the bing cash back and selling off the kit lens for $50, that effectively brings the body only price down to $800.
https://www.pentaxforums.com/forums/pentax-news-rumors/95112-k-7-18-55mm-%248...-cashback.html
In yet another thread, a Swedish retailer was speculating that a mid level body would come out this year. So who really knows for sure....
https://www.pentaxforums.com/forums/pentax-news-rumors/81158-what-comes-after-k7-14.html (post #206)