Did some investigations on the Catalina beta on the new Read-Only system volume and found some interesting things out:
1. There is a single APFS container on a physical partition.
2. The APFS container splits the prior APFS volume into 2 APFS volumes (<Volume Name> and <Volume Name-Data>.
3. The Applications folder appears to show in the Finder from 2 Applications folder: one folder in /Applications (user installed apps) and one folder in /System/Applications (Pre-installed apps).
4. The APFS System volume does not appear to be mounted read-only but rather protected by SIP.
5. You can still disable SIP using "csrutil disable" in the Recover partition. If you disable SIP, you are able to delete built-in apps and other things in the System Folder.
6. If you select the option to reinstall in the recovery partition, it started downloading the base OS image from the internet (or caching server in my case). I was expecting an "erase contents and settings" like feature on iOS, but that doesn't appear to be the case (at least at this point). It also doesn't appear to use APFS snapshots.
7. Boot Camp continues to be on a physical partition completely separate from the APFS container.
8. hdiutil and hdid no longer mount disk images in Terminal and give a "no child process" error. mount_smb continues to work fine.
(All testing was done on a T2 2018 Mac Mini).
