Little off-topic, but most newer DSLRs (Canon 5D mkII, Rebel XSi 450D, as well as various Nikon offerings and some other less-visible brands) are now including video recording - 1080p and of course, full support for each manufacturer's full line of lenses.
BTW, a lot existing semi-pro video gear has interchangeable lenses as well - even 6-7 years ago, the Canon XL-1 MiniDV cameras we were using at the digital-arts school had interchangeable lenses.
If you really want modularity, take a look here: I'm not allowed to quote web links!
The thing is that I don't have the thousands of dollars to buy any of the available interchangeable lens video systems on the market. I became frustrated with not being able to outbid anyone for the Canon L1 and XL1. This is precisely why I have chosen this route. By going to a smaller scale using the C-mount, I'm able to reduce my costs to where I can afford this system. So instead I'm building one from off-the-shelf components capable of doing what I need. And if I really had the money, I would want an Arriflex D-21!
Xavian-Anderson Macpherson
ShingoshiDao[/b]