- No direct access to filesystem. This is a huge concern for a few reasons. For one, it means that every Lua mod needs an associated omwaddon if custom assets are used. This may not seem so important at first but it has some pretty serious drawbacks.
It makes some advanced configuration impossible. If you want to add some music files so your fancy Lua mod can play some specific mp3 in the grazelands, it is impossible. If you setup some shareable config system, importing them from in-game is impossible. I could go on with this one for a long time, but I just want to make clear the filesystem is a big deal when creating cool mods and its loss will be felt.
- If saves cannot be created, deleted, and reloaded this makes any attempt at a different save interface impossible. A mod that wanted to do autosaves every 20 minutes and only keep the 10 most recent ones per player would be impossible. A mod that allowed you to take screenshots with a Dwemer camera and put them in a film for you to inspect and load from would be impossible. The same general issue arises when we can only exit the game with one specific button due to an Exit command simply not being available. It means certain aspects of the UI will be impossible to change, this doesn't sit right with me and certainly puts a huge damper on any creative ideas for otherwise ordinary systems.
- No network access is also a major issue. It straight up makes a chunk of mods/mod functionality impossible. In the grand scheme of things, most mods won't be using the network, but there are still a fair few who will need it. Discord RPC, leaderboard systems, loading remote configuration files, auto-update with a click, automatic mod downloads, saving configurations and saves to cloud, syncing weather & time, utilizing any web API. Again, I could go on, but I don't want to give too many of my ideas away
These features, while potentially incredibly dangerous and destructive to your system, also have the potential to do many "cool" and useful things (like in the examples I mentioned above) with little effort and that would otherwise be impossible.
If scripts could read from anywhere and write to their mod folder this would be enough. If REST APIs could be used, that would cover the majority of use cases as well. There are clear boundaries that can be set instead of just declaring unrestricted (or completely restricted) access to everything.