I am starting to plan out out some built in bookshelves or our office in our new home. This will be my first project of this size so I figured I'd come here to ask for some help.

Here is the picture of the wall that we want to put the built-in on. We're thinking some simple bookshelves painted to match the trim in the room so I am leaning towards just using some good birch ply and some decent trim. The wall is about 10' wide and the ceilings are 9' tall. (I forgot to measure the distance from the window casing to the wall, but will do that when I get home).
Wall.jpg

What you don't see in the first picture is the cold air return that is on the leftmost side of the wall (it's behind the mid-sized bookcase that is pulled away from the wall so the air still gets in). Here is a picture of the left corner of the picture above. The cold air return is 32"x8" and uses the drywall cavity as the "duct."
corner.jpg

So the first question I am trying to figure out before going down the path of a design is what to do about the cold air return. The way I see it is I have a few options.
1) Leave it where it is an build the shelves around it so that is remains clear for airflow. (Low amount of work by may make design strange)
2) Move it high on the wall and build the built-in to maybe 8' and have the return in the last 1' above it. (low amount of work but puts a big return vent above a nice built in and prevents the built in from being floor to ceiling)
3) Move the cold air return into the floor and perhaps do 2 of them. (moderate amount of work as basement is accessible, but means floor vents that can get things dropped in them, etc.)
4) Move cold are return to another wall. (lots of work and not really worth it I don't think)
5) Somehow figure out a way to get 1.7sqft of cold air return in the kick plate of the new built-in and routed to the existing returns. (no idea how hard this would be)

Anyone have any thoughts on what might make the most sense? I know this might be an HVAC question as well, but I figured folks here might have a good feel.

Thanks in advance for all your help and reading the post!