The problem with your estimate is, is that you forget Bitcoin isn't the best coin.
The other altcoins like Feathercoin and Peercoin use less energy/need less miners/have 30times faster transaction times/have more coins/better in every category. Might take another year or two, but the coins with the most benefits will be the higher echelon coins, specifically not Bitcoin(unless someone completely changes everything about it to make it better in every way shape and form).
Bitcoin is only extremely more popular for it's capitalization on early mover and early promoter in the beginning. Other coins will easily be worth more.
Bitcoin is the best coin in the eyes of rich people like me. The energy and miners need be there (the coin economics do not work without it), the confirmations are not reliable if they are much faster than Bitcoin's. "Have more coins" is a joke.
It is possible that there are fringe uses for other coins in the future, but to me it looks unrealistic that all the other coins combined would reach even 25% of Bitcoin's market cap. Main reason why anyone would think otherwise is that they don't have as many bitcoins as they would like to have, and want to amend that the easy way.