If First Mover advantage is lost, whether it takes years or months, it will be gone forever. Yeah, Bitcoin will still be around. Hell, MySpace is still around, but The escape route from Bankster tyranny will have been blocked.
Goldman sachs and govcoin can never replicate some of bitcoins best attributes:soverign, immutable, no KYC. and extremely unlikely to replicate other features that make bitcoin so great : limited , disinflationary.
Once you know this , you will have no fear of these private blockchains.
Who says it has to even be private? All they have to do is clone bitcoin and premine the shit out of it, market it as the drug and terrorism-free version (loss of anonymity is a feature, not a bug), and prop up the price for a few months. If they hire K Street lobbyists to encourage USG to treat their coin a little more charitably and our coin with a little more hostility, it's off to the races.
We'll still be squabbling over SegWit and 4MB when their nodes are the size of Google data centers processing millions of transactions an hour. They'll be like a hot IPO and we'll be de-listed and relegated to the penny stock pink sheets. And we'll deserve it.