I think that this may happen in the future. but this will only happen when altcoins have a good working product. but it may be the case that bitcoin will not become a secondary.
I believe that altcoin can never replace bitcoin anymore, altcoin is a bitcoin dependant and we all know that if bitcoin fall all other coin in crypto will never exist, because bitcoin is the heart of crypto coin and it is considered as a most trusted coin so if bitcoin failed every coin will also failed.
For now,i still believe that bitcoin will still dominate the market and even few years from now.Altcoins are just good for short term trading and then they just lost their value after some time.With bitcoin,it is still considered the mother of cryptocurrency and still holds the most expensive coin even if the crypro market continue to fall down.