What do you expect the gap will be in 2 years? If things continue for the next 2 years as they are the gap will be so huge that people will be buyung the ps5 as a snowball effect. Not to mentione the backlog of great games. In 2 years it will be to late. Its why I don't think the series will beat the x1.
Even if PS5 will track ahead of PS4 in about 2-3 weeks, Sony only has a chance to sell well in the next 2 years, after that they’re doomed. PS3 situation all over again!!