Create different realm subscriptions to where you are able to have different "size" realms for the player counts. Could be in different teirs from the original 10, and then to 20, 50, and 100 being the final end goal. The realms would be priced differently accordingly for what Mojang is comfortable with.
The reason for the higher cap is to bring even more players together on private worlds instead of servers, especially after cross play has been brought from all systems. 10 is a good number for very close friends but extremely limiting to those who have a big following, something that would greatly benefit streamers without having to create their own servers.
While servers exist already, the downside is the complexity and PC requirement for them. With minecraft being accessible on all platforms, its only fitting to have a similar service with similar capabilities for all to enjoy.
An example of such success is the Dream SMP server, only invited people allowed where a ton of friends end up creating one of the most popular minecraft worlds in todays time. Along with the huge community involvement for it between both streamers and players alike, having a similar system for realms where so many others can create their own huge worlds would greatly improve both popularity and the longevity of Minecraft.
(Originally posted on reddit 4 years ago, having realm caps from 20, 50, and 100, all being different teir levels for what you pay monthly.)