Chase Loot
Right idea - wrong implementation with Myth Drannor. I know this is a little different than what you asked for, but it's also very important and the devs have yet to acknowledge player concerns about this and state what their plan is going forward.
I am a fan of chase items and have significant experience with this outside of DDO from sports cards, collectible card games and miniature games. Chase items should not be the only way to get essential stats that many build would need. Spell critical chance and fortification bypass are examples of things that should not be exclusively chase items.
If you want to have a regular version and a chase version that is like 1% higher that is a great implementation of a chase item. It's not needed to construct a reasonable gear set, but power gamers will still go for it in the long run without feeling like it's a ridiculous chore or players are being forced into rerolls.
Affixes
There are two factors - one is how important the affixes are to most builds and the second is how easy they are to find alternatives ways. For example fear immunity is something that is available as an augment and through many enhancement and epic destiny trees. When I see that on gear it's rare I am happy to see it.
Here are my thoughts on affixes based both on importance and availability:
Affixes I dislike seeing on gear:
Quality Will Save, Reflex Save Fortitude Save - too small to be impactful. Individual quality saves should not even exist on items. +3 quality to bonus to all saves should be used instead, but even that will not be exciting to most players.
Reflex Save, Will Save, Fortitude Save - can't imagine anyone being happy to see these in current form. Only 1 higher than resistance so nearly all players would prefer a resistance augment..
Anything class-specific such as reinforced fists or Druidic Survival Mastery - there should be augments specific builds can use for these instead of being on gear slots.
Insightful Deadly, tactics - redundant with trance
<Stat> skills: Exceptional bonus - occasionally useful, but not often except for a trapper. Should just be an augment
Proof Against Poison: Does this even work - doesn't seem to provide any noticeable benefit?
Proof Against Disease: Does this even work - doesn't seem to provide any noticeable benefit?
Tendon Slice: Rarely impactful to justify a gear slot - better as an augment.
Competence Elemental Resistance: Rarely impactful
Immunity to Fear: Prefer to just slot an augment if I need this as so many builds end up getting this by default
Insightful Resistance: Just a downgraded version of parrying. Should not exist on gear at all.
Distant Incite: If a tank I will use shield throwing if I need to agro mobs
Linguistics: Niche thing for maybe an off-tank that over-relies on intimidate. Augment for niche builds is already available.
Physical Sheltering (prefer 1 augment vs. 2 gear slots)
Magical Sheltering (prefer 1 augment vs. 2 gear slots)
Acid, Fire, Cold, Electric, Sonic Resistance - not worth a gear slot usually - would prefer absorb as it's more impactful
UMD +x: Not really needed at end game
Putting Ranged and Melee affixes on the same item
Putting Martial and Casting affixes on the same item
Pact Dice (Should be an augment rather than an item slot unless it's a fully warlock item)
Affixes I am less excited about but are still fine
Anything I can get on augment - accuracy, deadly, combustion, etc.
Exceptional Healing Amp - not impactful except for maybe a tank
Affixes I often have trouble finding
Typically things that can't be found on an augment
Quality Deadly
Quality Accuracy
Quality Combat Mastery
Insightful Accuracy: not available in all trances so generally happy to see it.
Seeker, Insightful Seeker, Quality Seeker, Exceptional Seeker
Crown of Summer
Action Boost Enhancement
Insightful Armor Piercing
Insightful and Quality Stats
Insightful Sheltering ideally although I'll take insightful magical sheltering and insightful physical sheltering
Quality Sheltering ideally although I'll take quality magical sheltering and quality physical sheltering
Insightful <spell type>, e.g., insightful combustion
Quality Spell Focus (hard to find)
Sacred Spell Focus (hard to find)
Specific insightful spell lore items for types not included in the past life feat spell criticals such as negative, force, radiance that used to exist but seemed to be stopped since sharn. Alternatively just update epic past life spell critical to include these types which is actually better.
Insightful Spell Focus Mastery (hard to find)
Insightful Potency
Quality Potency
Exceptional Spell Power, Exceptional Lore
Force, Light, Alignment, Poision Absorb
Imbue Dice
Spell Saves and Insightful Spell Saves
Deception, Improved Deception, Quality and Insightful Deception - but for the love of all that is good Please fix these items so the bluff bonus actually works. This has been over-reported and discussed, but still never gets fixed.
In general I thought the trend of adding more augments for these stats with updates was a good a thing and was disappointed MD didn't continue this. Over time if you continue to add more augments for hard-to-find stats there will be less scrutiny on your gear.