It would be interesting to know what the rate of uptake on PS Now is. If it’s not very high Sony might consider a PS ‘complete’ sub that covers both Plus and Now, for a slightly higher price.
(It looks like Microsoft have already done this and it’s called Game Pass Ultimate, so even more reason for Sony to follow suit.)
From a marketing point of view, having a single subscription would be a much easier sell to customers.
Also, between buying games (physically or digitally), getting games for free through Plus and getting access to a catalogue of games through Now, I wouldn’t have thought many people had enough free time to be inclined to sub to more than one service; in a sense they’re competing with each other within the PlayStation ecosystem. Merging them would, I think, make most sense for both Sony and customers - a single, more expensive and better value service yielding a higher return per customer.