Although when some alternative coins start growing, the question of legitimacy appears. There are no obvious evidence and reason for Dash to grow. But price still growing, achieving $500 and it attracts lot of attention.
Also we can watch increasing interest of privacy-oriented currencies like Monero and Dash. Bitcoin still major currency but it has some problems with anonymity and privacy. And considering the attention governmental agencies pay to cryptocurrencies, there is no surprise that people look for more private currency.
But it is not expected that Dash will shift Bitcoin. People still prefer Bitcoin instead of Dash or other altcoins. Moreover people using many different coins do this for some speculating purposes.
The demand for Dash raised out of the blue, but Bitcoin will be major currency for long. Nonetheless Dash is not sustainable: it reached more than $500 and soon fell to $460.
It is also thought that price raising was provoked by stolen over $30M from Tether recently.
Although despite the total rejection, the price of Dash is 5,52% in USD and 3,65% in BTC now. Bitcoin grows up again, nevertheless the situation is unpredictable and everything can reverse.