I just yesterday thought "I wonder how long till we get an Istas book" (followed by "I wonder how much donation to that thing mentioned earlier would be needed to get an Istas short story in the meantime?..") so freakin huzzah for that!
It's a bit annoying not to be able to preorder the ebook, but I'm sure you'll remind me closer to the release date, and I'll be just as keen to buy it immediately at that point as I was now