Can you elaborate on why knockout is old and dated? It's HTML and JS, just like the others.
And compared to the bloat that is angular and especially ember, I find knockout strikes with simplicity and 'keeping-it-simple'.
It's not. And not everything should be architected as a SPA, but more likely multiple page SPAs. Your users probably don't go to every module of a large app with the same frequency...
Knockout + Backbone Router is all you really need. It will save massive headaches from trying to shoe horn something in to angular or ember.
Your app can out grow knockout and then your stuck rolling your own location provider,dependency injection and more.
2-3 years ago knockout was a breath of fresh air but know its just old and dated technology.