Is it five years already?! I remember the switch and it looks great.
As a Moveable Type user, chosen by my designers for I know naught about coding, I can just say that I have had a free version the full seven years of blogging, and it is in ‘php’, a change initiated a year or two after we started. I did worry a bit when MT made some admin moves last year but so far so good. If I was doing a fairly complicated design like yours, I’d probably feel differently, and I admit I’d like a redesign of my page – whenever my designer has time to do it.