I checked out the casement mechanism, can get pictures if you'd like but the upshot is that the window doesn't come IN at all and so doesn't affect what I put on the window from the inside.
So I was thinking more last night about the chest, window seat, etc. One thing I think could work would be to center the chest in the area (right now it's shoved over against the left wall), which would leave 3.5" inches all the way around. Then get a piece of good furniture foam (available at Joann Fabrics) cut to the size of the WHOLE nook. (As in, the chest is 21" by 48" and the nook is 28" by 55" -- so the foam would be 28" by 55" and extend over the edge of the chest by 3.5" on all sides, while filling the nook completely.)
I think 3.5" isn't enough to cause problems when sitting on it, in terms of falling through or whatever.
Then I'd do a bunch of throw pillows, just kind of scattered around the whole nook. (I especially like the idea of having some against the right side of the wall). I think I would use a dark third color for covering the foam (I was thinking a good saturated blue, maybe even denim -- I do want to de-frou-frou a bit) and then also for throw pillows, but do the throw pillows up in different kind of weird/ eclectic patterns. For example, rather than using the curtain fabric for a straightforward pillow, cut out a bunch of butterflies from it and applique them, plus using various fabrics I have (antique kimonos, saris, sari borders*.) Idea would be a colorful eclectic mishmash (sort of Anthropologie-ish) that relates to the curtains on the four-windows but doesn't echo them too literally.
Then a window-contained covering (wood or bamboo seems most likely at this point) and weird photos/ pictures on the wall on the side.
What do you think?
Only bad parts I can think of at this point are 1) mooshing the edge that sticks out on the front, since we'd sit on that with legs dangling (could fix by getting a piece of wood to put over the chest and under the foam, but that adds expense and height -- would like to keep the total height under the window frame) and 2) it would hide the top of the chest, which I do like.
(One meta-recognition as I have been thinking about this -- I don't think it's fully dawned on me that this is MY house. It's the first one we've owned and I always have this thing in the back of my mind of keeping the landlords happy, keeping it pretty -- my own taste [and, importantly, E.G.'s] is more weird/ edgy and a bedroom is a good place to experiment with that a bit, since it's pretty private -- casual visitors won't see it.)
This would start to add up but not too bad -- maybe $50 for the shade, similar or less for the foam, I'm sure I could find good fabric for a good price and would need only a yard or two depending on width, and then I already have the rest of the fabrics I'd use.
*I have a lot of textiles that have have stains, tears and other problems but then also stretches that are perfect, so I can't use the whole thing but can cut them up for this sort of project.