In my opinion, in medium term, I can see a strong battle between altcoins in order to reach the second and third position, in particular between ETH and EOS. BITCOIN will continue losing "share" in the total market but I don think it will lose the 1st position this year, neither the next one... In three years from now maybe.
You know, BITCOIN is becoming more and more scarce and that is giving an added value which cannot be balanced by altcoins as XRP or XLM for instance...IMO. It is like GOLD nowadays...
ETH has to solve many aspects regarding scalability and transaction speed as well so, the only possible candidate to take the lead could be EOS but, of course, in this case there is more speculation and expectatives based on the performance of similar coins as STEEM or BITSHARES than real facts... I think that the last quarter of this year is going to be definitive in terms of COINMARKT leadership place.
Steem on!