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Not sure that your example proves that YC is no longer interested in RFS #5. I think RFS# 5 covers companies that could be huge, but I'm not convinced that I would ever want to code on a tablet.
RFS #5 has nothing to do with the essay linked. See http://ycombinator.com/rfs.html for all the "Request for Startups" bullet points. Personally, I think it's a dumb RFS to begin with. From a professional standpoint, I couldn't handle developing on anything else but two 24+ inch monitors (if not three) and a mechanical keyboard. Not that I couldn't do it on a laptop or tablet, it just makes me about 300x more product…
I think that in the future it might be possible that developing on a tablet might just mean hooking your tablet or other sub $300 device up to two 24+ inch monitors. Think developing iPhone apps from a $25 Raspberry Pi, thanks to the cloud :-)