In the anticipation of a QUIC and HTTP over QUIC standard I'm wondering if HTTP/2 will only be an interim protocol, which will be around for 2-5years, but will no longer have a benefit after that.

I mean HTTP/1[.1] will basically be around forever, since it's super easy to implement, works without encryption and is supported everywhere (dozens of libraries available). HTTP/2 however is already hard to implement compared to that - it needs an ALPN-ready TLS library, and flow control and multiplexing is not easy. If it also has less benefit than QUIC (which will also be hard to implement), then it's questionable why one should still implement and deploy it in the future.