I am always trying to manage customer expectations. The sonicTransporter i9 is the fastest commercially available Roon server so typically everything in Roon is near instant when you have one as your Roon Core.
The biggest problem with Roon and extremely large libraries is performance. Once you go over 200K tracks things like searches start to slow down. I have a customer with 1.2 million tracks and searches can take 10 to 20 seconds. This would be completely unacceptable to many users but this customer recognizes the limitation.
Also with very large libraries you need to start optimizing other parts of your setup. For example you need a good network and either store all your music on the internal SSD or use a very high performance NAS if you use a spinning Roon performance would be almost unusable.
If anybody is interested in discussing using Roon with extremal large libraries you can contact me using the smallgreencomputer.com “contact us” button.