I am storing a couch in my quilting room. It, in turn, is "storing" some quilt tops while I decide how to quilt them. It also sometimes has little piles of fabrics for specific projects, while I'm "sleeping on" whether I like the fabrics together. Don't worry. The window seat will get used. The light will help with both of the things I mentioned..
It would also maybe be a nice place to sit while you're using the light at that window to compare fabrics for your quilt, or to (don't say it!) frog stitch something. Or whatever.
I really think a window seat is an inherently useful item in a quilt room. We all need one! Thankfully, you have one ;-).
Have fun!