The bitcoin infrastructure is actually not that small. KNCMiner quickly sold-out 1,000 Neptune miners for $16,000 each. Thats $16,000,000 just from one product run from one company. Multiple this by all the other mining companies and all the various iterations of mining products, and the total USD invested into just the bitcoin mining infrastructure is most certainly measured in hundreds of millions of dollars. There's about a quarter million bitcoin nodes (at let's say $500 per node hardware cost = $125,000,000), and numerous services design to mesh with this infrastructure and the bitcoin protocol.
This functional network of expensive hardware and well thought-out software will not just be "tossed aside" or repurposed.
Hear hear! and at $5000 a BTC I think the value you sink into a protocol just to carry and store your wealth starts to be questioned, i.e., why wouldn't I use another, similar protocol at these high valuations? Also someone else can come along when BTC is approaching $1 Trillion market cap, and easily afford $100 Million to upstart and market a better coin with the infrastructure in place.
I'm hedging more and more with Litecoin as the BTC valuation increase. Plus you gotta know it's coming to more exchanges soon.