My gut tells me that Apple is focusing more on the performance of the mini, and moving in the direction of a high performance desktop in a package that can't be beat.. but the price will probably fall in line with a base MBP by the time they have achieved this. Form factor is already there- and if the optical drive is done away with, there will be a lot of room for serious upgrade in the same form factor currently attractive to the market.
I just say this looking at the advertising, more emphasis on what you get than on how affordable it is. There may always be a mini with base specs of a macbook to bring along switchers and students- but I expect that within two years folk's won't be getting an iMac just for the performance boost. They'll be getting a Mac Pro to do that. The mini may fill the gap that many have been clamoring for, a mid priced well spec'd puter smaller than a refrigerator and bigger than an oreo cookie.