I don't think I'll ever "need"to upgrade. Over time, entry level camera's will get better and better, just as the high end ones will. And I don't plan on getting into the high end game (those women are too materialistic) :G
Really... I don't about your past camera history. But atleast I never thought a year back that I would be considering move from P&S to SLR. And you can certainly say the P&S have also gotten better and better in last5 years or so. That did not stop me from making this huge technological jump.
What Pentax has in offering in future is pure speculation and wishful thinking. Whereas, what Nikon (and Canon) will offer 3-4 years down the road is much certain.
Don't take me wrong... I surely believe that K100D is an excellent model. But Pentax is just not the right system for a long-term commitment.