I feel confident that WordPress will be more widely used than Medium next year, in three years and in nine years (which is an eternity in tech). Would you bet against that? I don't mean money, but if you feel confident taking the other side, we can both set calendar alerts and check back in one, three and nine years to see who was over-confident and who was appropriately confident in their opinion.
AFIK, no open source ecosystem with WPs level of usage has ever died (and in a sense OSS is unkillable), but it would be fun if you want to take the other side of my prediction. This kind of dynamic is why I blogged every tech stock I bought (after AAPL in 2001). It keeps you honest in your own thinking.