Cinnamon is interconnected with Mint packages, and Mint packages are interconnected with Synaptic. Mint doesn’t interfere with the base packages from upstream (Ubuntu), but Cinnamon 4.0 is for the moment is made to work with Ubuntu 18.04.1. Now, that Ubuntu 18.04.2 is released they’d test that on it to see, if their packages won’t break. If there’s something wrong (by Ubuntu’s base update), they’d correct it and release Tessa 19.2 in a month or so.
Quite naturally, they are keeping an eye on Disco packages, but won’t talk about it and/or release any solutions yet. They’d do the same with upcoming Ubuntu 19.10. In about a month or so, after the release of Ubuntu 20.04 LTS, they’d release the next Linux MInt LTS. By that time, there might be Cinnamon 5.0 or 6.0, and whatever they’d have would work quite well with Ubuntu 20.04 LTS base.
Upgrading 18.04 base all the way to disco is easy, but installing Cinnamon 4.0 packages in Ubuntu disco is not that easy – lot of dependencies not available in Ubuntu repos, even though they are upstream. You have to get them from different places. It is quite a bit time consuming work. Not worth the time lost. Much easier to move the whole thing to disco. Any future changes to Cinnamon would come through quite easily.
Actually, the people who like Cinnamon won’t come here. They’d just install the latest Linux Mint. It is not like the Arch, Gentoo, Fedora users creating the latest Cinnamon for their platform.