I think he would have a hard time doing so because he has quite short hands and my hands are quite long, so he doesn't have the capability of reaching as far between the keys on the piano as I do. This means he'd have to be so much faster just to play the same parts, and a lot of what I play pushes these limits even for me.
Getting into a further analysis of the playing styles, he tends to play things closer within the same notes of each other, and he usually doesn't play notes that are very far apart without playing something else in between first. He tends to move up and down doing runs instead, but rarely jumping more than let's say to the minor third or the dominant before moving somewhere else from there. He also uses more of a percussive playing style than me, while I do many jumps and runs, scales and patterns over a wider range of notes, for example I'll play from the root to the dominant to the ninth with the same hand and then something else with the other hand.
These are just different ways of thinking and different playing styles, but physical limitations are also a factor when playing far-in-between notes like that. My impression is also that my style is a bit more polished than his, but different things work for different situations and I probably wouldn't fit in musically with Arcturus any more than he would fit in with Winds.
In all honesty the Arcturus guys do have a less polished and more rough-around-the-edges playing style compared to let's say Carl, Lars and myself, but that's not necessarily a bad thing either as it adds a nice and genuine vibe to the playing, it definitely becomes more "rock 'n roll" this way, and it works very well for what they are doing. But it wouldn't work when playing the music we do in Winds, which requires a very polished touch.
This is not to say that one is better than the other, but the Winds guys and the Arcturus guys are from completely different schools, so it's hard to compare. I don't know what Steinar's limitations are, but I know mine, and I would not fit in playing let's say "good old rock 'n roll music" because my musical mind is much more progressive and classically oriented, so I would overplay and totally over-do it.
I'm not saying that Arcturus is rock 'n roll, but just using that as an example. At the same time, I think one would need to have a very classically minded piano player to follow my way of thinking as far as how I arrange my keys, and the fact that my playing style is also very unique and very different from most key players who play in metal bands, this makes me think that we are just too different as players to do each other's things. Even so, my guess is that I'd probably have a better shot at doing his stuff than he would have at doing mine, for reasons as stated above.
Regards,
Andy