At which point everyone would complain about the price.
Many laptops have Express card inputs.
I don't know many people who'd want to mount a laptop to a tripod given the risks to the laptop but if there were such a demand some 3rd party would be likely to do this.
Video input meaning ???? Many laptops can capture video through various means. You're certainly not going to find one with HD-SDI inputs but there are 3rd party devices for that.
Some folks even wonder if Sony would come out with their equivalent of the P2 Store for SxS. Given the cost of a P2 Store, a laptop can be had for the same price or less with many more useful features. On the other hand there are certain shooting situations where a device like that would be space and power efficient even if it cost as much as a laptop.