I'll just quickly add that it's my understanding the 787 was not an attempt to answer the same (perceived) market demands as the A380. The 380 was a long-term approach to a changing market, airport congestion etc - a better version of current VLA options (their own admittedly-obsolete 340, and B's 747s) to a new extreme. Maximized pax-carying ability with a singly landing/gate slot.
The 787 was simply the way of the future - everything from tri-jets to A300s, Boeings own 767s, plus almost everything else on the market had the potential to be upgraded and streamlined with a 787-type aircraft. Many of those older types were going to be retired in the very near future during the program - of course huge delays threw a wrench into the entire retirement/replacement idea.
That aircraft really didn't have much to do with the A380 at all. The bulk of future designs and sales will follow the basic formula of the 787 moving forward. I think AB knew this, they just waited a little bit (which probably saved them hundreds of millions ironically) and EIS of the A350 (in the grand scheme of things) was similar. I don't think this hurt at all however, on the contrary - the largest variant of these types, the A350-1000, is about to fly in revenue service before
the largest 787.
As for future 4-holers. No.
You'll see legacy cargo 747's forever, a few old A340s, charters, etc.. EK's 380s have a strong future, at least with them. As far as a NEW quad is concerned, I believe the only hope for this concept still remains solely with an updated A380. I'm about 50/50 right now. If you look at population density, air travel increases, etc - it simply doesn't add up, eventually you're going to NEED more VLA-type aircraft, and there's a lot of additional flexibility with the 380 design (it was, after all, DESIGNED to be bigger).
If someone held a gun to my head and made me choose, I'd say low-rate production 380 for the next decade, then a (fairly) quick EIS of a new NEO/stretch/wing/etc 380. But no, I don't see Boeing being in a position to launch a program with that risk level. It would need to be a full-length double-decker. If there's a future for the VLA, it'll be all-Airbus, but we won't really know till population levels become overbearing - sounds like fun huh?
Just my $.02