Hey, that's a great idea.
Mind if I throw in some "buts"?
I sew a lot, and I found you don't need a lot of space in front of your machine, rather in the back and to the left; when you sew a lot of fabric you can hold it in your lap, but after passing under the needle it has to pile up somewhere. Judging by your fabrics I'd say you're more into patchwork and small things, but even so I fear your makeshift-slideout won't hold to well the weight of your machine, even more so when going full speed. So I'd invest in a larger shelf, even coming out a bit, but properly installed and secured.
If you like you could also add a threadholder in the back, over your machine - just a lot of pegs on a board, to slide on the spools. Makes an interesting, colorful addition too.