I am using Realm Object Server 1.8.3 manually installed from a .deb file (found on packagecloud.io) on my Ubuntu 16.10 and I would like to upgrade to a 2.x release (2.5.1 is the latest at the time of writing).
Unfortunately, packagecloud.io does not have 2.x packages (except some 2.0.0 release candidates and alpha versions) available and the installation instructions are using a different mechanism and do not integrate with systemd as far as I can tell.
Any hints on how to best do this or where to find a package?
There's no .deb file because ROS 2.x is published as an npm package. While you're right that there's no integration with systemd, because it's an npm package, you can use pm2 to daemonize your install (pm2 integrates with systemd).
Before you can daemonize it though, you'll need to follow the step-by-step guide on upgrading ROS 1.x to 2.x (won't repost it here as it's fairly lengthy and may become obsolete as new versions of ROS are released).
After you've done that, running it with pm2 is fairly straightforward:
npm install -g pm2
pm2 start path/to/myserver/dist/index.js