The incentives to group up while questing is something I'm really missing in ESO. If I go questing with someone, it is absolutely no fun when a difference in movement speed turns into an annoyance forcing one to wait for the other rather than an asset when dealing with the enemies. And "forced" incentives like needing 2 people to step on pressure plates to complete a quest is not the solution.

My proposals for future changes in regards to overland difficulty:

1. Introduce a difficulty setting that people can adjust individually. Internally (i.e. server side) it reduces your damage done and increases damage taken, and to maintain the sense of fighting tougher enemies rather than just being debuffed, display your damage numbers client-side increased by the same number by which they were reduced server-side, and increase displayed enemy HP by the same factor. Create loot scaling so that people playing at higher difficulty can still get the same out of their play time as those playing at a lower difficulty. This way people will be able to pick their own setting and still play together in the same instance with the only immersion-breaking observation being that some players (who are playing at a lower setting) appear much stronger than others.

2. Give people easy access to medium and long duration CC (put those skills in soul magic or fighter's/mage's guilds or maybe some new active skills in legerdemain) so that people can control pulls consisting of multiple mobs. Give those abilities some downsides that would make them undesirable in PvP (2s cast time, target becomes immune to all attacks, enemy gets resources back quickly or gets healed while affected, breaks on any damage the target takes etc), or make players just flat out immune to the new skills to not cause balance issues. This will add depth to the existing content at higher difficulty settings without any drastic adjustments to the entire content, because now if you play well, you would be able to "lock down" enemies that would otherwise overwhelm you while already being challenged by the ones you couldn't lock down.

3. When designing new zones, create enemies with greater variety of difficulty and mechanical complexity. At lower difficulty settings everything but bosses would be a faceroll, at higher settings on the other hand you will encounter enemies who are fairly easy to handle, and those you can't do by yourself (or even require a full trial group at the highest difficulty in some cases), giving you incentive to go questing with friends or even allow you to just meet strangers on the way and continue on with them.