I think its fair to say that most people (especially those used to system reqs for the FPS genre - those are really getting ridiculous) should be ok. I remember playing AOK years ago on a so bad that i had to turn what few options (seems like few now...was a decent amount then) down as far as it could go to play without framrate issues. And then AoM came by and i slowly progressed up its graphics ladder (everything on low, to about medium, to about everything on high - speaking primarily of resolutions ). It seems to me that ES games have a tendency to last (still play AOK occasionally with some friends, just for fun - and the point is its still fun), technically and with regards to gameplay. So i'm optimistic about this game as well.
I have to admit i am a little worried about a seeming trend of RTS games getting more graphics intensive (just looking at the horizon - AOE 3, Rise of Legends, Earth 2150, not to mention current games like Dawn of War.) But most RTS developers, and especially ES (thus far, at least - and no reason to expect them to change for the worse), have made their graphics options quite scalable, thankfully. (but scalable or not, the new SSSI game has me worried about how graphics intensive it is...but it looks like its almost half FPS). AoE III's graphics are absolutely stunning, but i am sure scaling down elements (hehe...such as radioactive swans, lightsabers, ice cream hats ) and similar options should certainly help computers that may have even trouble with recent FPS games at lower settings. Of course i am purely guessing here....but guessing hopefully.