True. Now bitcoin is the best currency. But that's not it's day job. By day it does yeoman's work as a p2p transaction protocol which preserves a transparent global general ledger.
I think any successor to bitcoin will build on top of the bitcoin network. It's the worlds largest supercomputer. You'd have to be an idiot to throw away the worlds largest supercomputer.
I like to keep my savings in the most secure storage vehicle which current technology allows. A successor to bitcoin will need to be just as secure, in order to compete. That means either it uses the bitcoin mining network, or it spends a billion dollars building a competitive network.
Layered protocols will enable smart contracts, legal custody proof, provable notary services, p2p currency exchange, and an unknowable number of new applications. This is like the advent of the LLC or double-entry accounting. It is a game changer. and first movers will grab the land.