Just my two cents, but I see the Docker limitation as not necessarily a bad thing.
From an infrastructure point of the view, the whole point of the cloud is to scale horizontally, not vertically. What that means is that it’s more efficient to have four 2 GB servers with 15 websites than to have one 8 GB server with 60 sites.
This helps with scaling where one site may increase in traffic and affects neighbors on the same host.
Also helps to prevent a single point of failure in which your 8 GB server goes down and takes 60 sites with it.
It also helps to plan for growth by keeping servers at about 75% maximum planned capacity (75% when ALL sites have a constantly high load - Disk, CPU, RAM and so on).
MariaDB and Redis both take up memory, so overloading a single server with many sites will lead to bad things. On that note, Docker’s limit in EE4 helps to push users towards using a separate server for their database, which again is good practice after a certain number of sites, and even towards more advanced concepts such as load balancing.
However, it’s really up to the user to add as many sites as they want to their own server, and feature requests are feature requests at the end of the day.
AFAIK it’s possible to increase the number of networks by manually controlling the subnet creation, using conservative values etc. within Docker’s private IP range within Compose. Might be one approach that EE takes in a future update.