It would be possible to get 30+ fps from a DSLR, but it would cease to be a DSLR. The sensor (CCD/CMOS) gets hot - not hot enough to burn you or anything, but each individual pixel gives off radiated heat to the pixels around it, resulting in "noise" - the digital equivalent of grain. This is most apparent in long exposure times.
Transfer from sensor to storage media is a 3 step processing. capture->processing->storage. The image is processed in the "buffer", then sent to the media card. Some memory cards are better than others - 80x is about the standard now, that allows continuous 2-3fps from a 6MP Nikon D70. I don't knwo for sure if, at 80x, the restraining factor is the bandwidth to the card, or the camera processing the image.
From my understaing, if you set a 12MP camera to shoot at 1MP, it actually takes a 12MP image, converts it to 1MP, then sends it to the card. SO the best way to do this would be to take a modern camera body, fit it with a low-resolution sensor, and program it so that the shutter can stay in the up position and the electronics turn on and off the data flow from the sensor. This would result in a low resolution, high-speed camera. In other words, a very expensive, very crappy video camera :).
IF you want DoF, the best way about it rigth now seems to be the Canon XL series cameras. The XL2 has an adapter to use EF series Canon lenses, which are what the current line of Canon SLR film and digital cameras use. This should get you the DoF you want (with the proper lenses). You're looking at about a $10k setup by the time you buy the XL2, XL->EF adapter, and appropriate EF lenses.
O yeah, and with EF lenses, you can get "IS" - Image stabilization. That would be rather nice on a video camera - kind of liek a low-budget steadycam.