Don't know if this information will be helpful, but I just installed 10.15 over 10.14 on my mid-2014 MacBook Pro.
The installation appeared to proceed normally until the final boot, which did not complete. During a normal boot the progress bar would get up to about 75% and get stuck there. Safe Boot worked properly.
Tried everything I could think of myself first, then found a solution that worked for me (delete the .kext files from /Library/Extensions). The original thread is here:
In my case, I moved the files from /Library/Extensions/*.kext into a temporary directory just in case I wanted to put them back. The system wouldn't let me move something called AppleMobileDevice.kext (I got a permission denied message even when using sudo). That's the only thing left in the Extensions directory now.
Over the past hour I've been testing my usual daily apps and workflows and everything is operating normally. Computer feels snappy and the temperature is normal. I was concerned that apps wouldn't work without those files, but no problem so far.
Yes, they will run as the did on Mojave..., but Apple wants to move all of them to the new framework System Extensions.
What they intend to do is to deprecate the kind of extensions as they release system extension frameworks of the same type. First of all will be Driver Kit and Network Extensions, so in a future release after Catalina (around fall 2020?) all kext of those types need to be migrated.
There are other kind of kexts (like system monitor ones to display CPU status, voltage, etc) that will be also deprecated after that when they release support for them under system extensions.
So it seems the process will be slow enough to give time to developers.., there are thousands around!
Finally, beta 1 has a couple of bugs on kernel extensions loading utilities (reported on another thread and to Apple) making those extensions explicity allowed to run (AppleKextExcludeList.kext) to not work... This happened on Mojave first betas too, so I imagine they'll fix that before final release.
More about this here: https://developer.apple.com/videos/play/wwdc2019/702/