Can we expect altcoins to reach the success of Bitcoin? and how long would it take? what are success metrics?
It is not easy to compare one on one these coins but Bitcoin is in no way superior technically speaking (and some times it can easily be considered worse!).
Technically speaking most innovations happen in altcoins since it is both:
easier -- they don't have to support compatibility with the large infrastructure that Bitcoin has nor convince so many people for a change
and safer -- not so much money at stake
Having said that, the altcoin experimentation have greatest risks, could lead to new unexpected attacks and so on. Bitcoin learns from altcoins and can implement some of the features (some cannot without overhauling the system) in the future if they prove successful without risking much.