My concerns are numerous
TLDR mods are complicated. Consoles are simple.
- More options = more player base fragmentation. More fragmentation = longer matchmaking times
- Mods can’t be made on the Xbox, they have to be done on a PC, so you need a mechanism to publish from PC to Xbox. 343 then needs to make sure this mechanism isn’t exploited for malicious purposes
- Related to the above, 343 needs to protect the client side code in console matchmaking from being modded by the mechanism in #2
- Also related to #2 above, there needs to be a way to make sure all players have the same mods active on their local machine before they can play together. This isn’t something console players are used to dealing with
- There are concerns around making sure available mods are all compatible with each other, or else players can inadvertently break their game.
This is a bit late, as I haven't checked this thread in over a week, but I'd like to address some of the concerns you've listed. I'll refer to them by the numbers you've listed them under.
- While I would agree in regards to the "mod playlist" idea that OP mentioned (I don't personally support that idea), if multiplayer mods are made available, they'll almost certainly be for Custom Games only. Remember, 343 is adding a custom games browser to MCC eventually. I imagine that would effect playlist populations more than mods would, but it's happening. Ultimately I think when players want a competitive experience, they'll go for ranked matchmaking. When they want a more casual multiplayer experience, they'll go for either the Match Composer or the soon to be added Custom Games Browser. When they want PVE, they'll go for Campaign, Firefight, or Spartan Ops. In my view, having optional mods available as extensions of existing parts of the game is unlikely to effect whether a player is in the mood to play those parts of the game to begin with.
- There are games that already do this, such as Fallout 4 and Skyrim. In those games, the developer determines what mods from PC are available in the console mod browser. As for potential exploits, just make sure mods are separate from matchmaking or anything that grants Achievements, XP, or Season Points (in the new progession system coming with Reach). For instance, the campaigns would be moddable, but those would effectively create separate builds of the campaigns from the official ones that you can unlock achievements from.
- I would basically give the same response from the previous paragraph, but only add that anti-cheat measures are something that are already being implemented on PC.
- This wouldn't be so different from if a player lacks the proper DLC in a game. In MCC for instance, if you don't have ODST, then you can't play ODST co-op with someone that does. The game would just check if all players have the same mods activated as the party leader.
- Other console games that allow mods manage to deal with this issue. 343 probably wouldn't feature mods in the browser that effect the menu UI, so if the game crashes when certain mods are used together, players can just load up MCC again and figure out a combination that doesn't crash the game. MCC crashes right now sometimes, as do other games. It doesn't permanently damage anything. They can just display a message when you open the mod browser that tells players that certain mods may not work as intended.
To reiterate, I don't believe that mods being made available on console (if implemented correctly) will negatively effect anyone's experience. Those who want to try them out can do so, and those who don't can ignore them. I should also note that community created mods can give a game almost infinite longevity. Halo Custom Edition has been completely sustained by it's community for more than a decade, with no official developer support whatsoever. If lots of cool mods come to MCC on PC, and console players are completely left out, that could convince some console players to migrate to PC over time, further shrinking the Xbox player-base.
My point is that although there are challenges and technical hurdles associated with making mods available on console, mod support is ultimately a good thing for MCC, and a good thing for Halo, on both console and PC. It's healthy for the game's longevity, and helps foster a sense of community, just like all user-made content in Halo, from Custom Games and Forge maps, to screenshots and Theater clips. The community helps keep Halo alive, and mods can help keep the community alive.