1 altium has spice on board.
2 matched net lengths, differential pair routing , bus routing, vendor integration , board variations, collaborative design , channel based design, and much much more you wont find in the sub 5k programs.. Or even the sub 20k programs.
3 altium originally did that but they moved away. The risk is massive data corruption. Why make a virtual filesystem in a file ?
4). I only have one wish for the ultimate cad/eda package. A telepathic interface. So i dont have to sit there fudging with the mouse and 3d navigator and endless pushing and shoving to make the computer understand what i want the design to look like. Telepathic interface solves that as the computer can clone the image i have in my mind. I also want fpga's and processors with telepathic interfaces so ican 'connect' to the fpga and 'think' i need 5 pwms , a bus here. , that there , this needs to works so and so , and the fpga reconfigures itself on the fly.
Anything else is just make-do and a drag....
Actually lets forget all that computer crap. I want a universal electronic component that is reconfigurable to become anything i want it to be. I'll call this a 'cell' and just like in nature where the dna tells the stemcell : you become kidney , you become eye , you become skin , i can tell these cells you become an led , you a transistor ,you a rocker switch and you become a nice polished marble case. Now go do it.