The advice in older books (i'll admit that I read little, George wilson relayed it to me) is that the bark side is to be out on planes.
There is a gigantic difference in durability on the flatsawn face vs. the ray side on the sides of the plane (extremely noticeable even in hand sawing and planing).
The ideal orientation of the grain isn't really for any of that specifically, though (if the orientation is wrong and the sole wears fast, you can just true it more), it's to deal with wood movement. Beech is a terribly behaved wood, it's a little bad even when steamed. I'm hoping any twist in this plane will be limited to tiny amounts, and the issue with twist is that it's seasonal. So if you true a plane in the dry season (winter here) and then summer comes around, it will twist out of true. if you true it again in the summer, it will do it again going back in the winter. That's really annoying.
if you can manage to get ideally sawn wood, that behavior is really greatly reduced (even ideally sawn billets like this can move a bit lifting their toes a bit with seasonal change, and then going back. That's not nearly as bad as twisting).
I've gotten to this point by not paying for ideally sawn wood (this wood is $16 a board foot whereas there are beech trees growing all around here that I could probably beg, borrow or steal if I could catch them falling over before they spalt). I've had dead quartered wood on both ends before that looked great, but when viewing from the top, you can see that it wasn't cut with the pith centered along its length......and it twisted badly.
There are other woods that are worse (apple) and I'd bet the steamed euro beech behaves better.
For a jack plane, this much concern may be nonsense, but the person who asked me to make this plane (or gave me specs after I offered when they gave me something I really treasure and wouldn't have otherwise gotten) said they wanted a shorter jack plane that they intend to use as a smoother.
Maybe they've been influenced by david charlesworth!!