The drain line follows the plane of the trap and goes through the joist at the top of the photo - the angle of the photo makes it hard to notice.
The "2 90s" to which you refer are in fact a T and a 45 for the vent which goes off to the left in the photo.
The only clear bit of copper pipe that I can cut into is the riser from the trap. But I think that'll work because I have enough height, as I explained before.
The toilet line worries me more because the coupling and new ABS bits would move the flange over by 3/4". The new narrower toilets will have no problem fitting in the space available: What does concern me is whether or not folks would notice that the toilet is a little closer to one wall than the other. Is an offset flange, then, a sensible idea, or does it present its own set of issues (greater risk of blockage?), or is it just not worth bothering about?
I'm sorry, I see my eyes were playing tricks on me...:o
On the toilet if they have an eye good enough to see the 3/4" off center, and are concerned about it, well, thats their problem. I wouldn't use an offset flange. I do however, highly recommend that you use an ABS flange that has a stainless steel ring on it, installed on top of the finished floor. Also use #12 stainless steel or, brass screws long enough to grip through all the floor and sub floor.
As long as you have at least the 15" either side of the drain to meet code, I woudn't worry about moving it over a little.