Was obvious long before Gamepass that it'd happen at some point. Content has been moving to subscriptions for a decade.
If Sony don't make any weird decisions and market it properly then it'll be massive quite quickly. They have the Disney+ advantage of having huge quality back catalogue, and a huge base of people who could access immediately. Even though they don't plan to put big exclusives on it day 1, they will hopefully provide a decent discount to those who are a subscribers to help justify the cost. Knowing Sony it'll probably put their 1st party games back to £60.
Interested to see if they put it on mobiles, PC, smart TVs straight away.