I've been working through issues around upgrading project from Unity 5.5 to 2017.3. This will also lay the groundwork for a future upgrade to Unity 2018.x whenever this is out of beta and proven stable.
Edit: See second post for further updates.
Following are some notes on what I need to fix so far. I might add to this over time if I find anything else. Documenting here so contributors are aware of the process and that an upgrade to 2017.3 will be coming in future.
- MCS iCode Compiler - Probably the main issue is the MCS compiler is broken in Unity 2017.3. There's a manual workaround for this here which works well for game to build and run normally. Assuming that mods will continue to work as normal as the "mcs.dll" itself is uchanged with this workaround, just an alias is being added. However, it's still necessary to patch the .csproj every time Unity generates it. There's a way to automate this as well, but I'd prefer to see a proper fix patch from MCS code maintainers before pulling the trigger on this upgrade.
- Materials Suddenly Specular - The default materials now have a tight specular shine without any mods or changes in place. Assuming this won't be too hard to fix and I just need some updates to how procedural Standard shader materials are generated at runtime.
- iTween Deprecated Calls - The older version of iTween library (used to move platforms, doors, etc.) is calling some now deprecated functions. This is easy to fix by either updating iTween or just commenting out deprecated functions. None of these are used by Daggerfall Unity anyway.