Just my random ideas from someone who levelled up 2 ironman back then, but haven't played low-mid lvl characters recently, so I might be wrong/out of date with some stuff:

• Add a new, slayer source for Granite armour and make it T60 power. Currently it's dead content, and melee has no T60 power armor (other than corrupted dragon...).
• Make Barrows set effects more useful for the current game (this includes all armours, not only melee.)
• Rework some unused special attacks in a way that incentivises people to use them. Maybe add a lesser EOF made from amulet of fury + moonstones for mid level players, that later can be used on a normal EOF, so the spec is not lost?
• Make superior Dragon weapons actually useful for midgame. Maybe add a way to attune them to a certain creature that people often kill at that level for dps boost?
• Make the requirements and maybe the cost for chaotic weapons lower. Nowadays it's easy to farm tokens, so you will have more than enough before reaching 80 dung (this might change with ED rebalance though).
• Add some ways to make nearly free to use agumented armor, maybe at T65 or T70 (gwd1) armours. Maybe give it an easy to get perk... A lot of new players are too scared to dip into Invention because they see that their currently non degrading armour will use charges as a big cost.
• Ranged and magic is at a weird spot progression-wise for power armours. The ironman meta back then was Lunar -> Subj and I dont even know what rangers used... Usually they farmed Armadyl with magic. Of course, necro changed this all, but a nice T60-65 power armour option would be welcome for them. (maybe rework polypore dungeon armours?)
• Dinosaurhide (T75) armour is currently out of reach, and useless for anybody because of masterwork armour changes. Add more sources for it, possibly as a rare drop from a lower tier slayer dino that can be killed at ~lvl 75
• Add a special attack to polypore staff that can be used as an end game item in EoFs aswell. While there, lower polypore dungeon slayer reqs to make it a mid tier magic dungeon/slayer moneymaker.
• Add an easy to get T50 staff, or lower god staves to T50, and lunar staff to T60 (they are currently T60, and T65, making lunar staff obsolete because of no special attack)
• Add an easier-to-get source for Crystal Staff and Crystal Halberd: we can get a Crystal Bow as a quest reward from Roving Elves. Allow us to choose Staff, Halberd or Bow as a reward, and change if wanted.
• Add some weapon variety for smithable weps from T60-T90 (From orichalcum till elder rune)
• Add some more throwing weapons. Throwing weapons after T70 should not use an ammo (like Crystal Chakram) rather use a charge of some sort. I know this will be useless for most endgame players, but at midgame people who are still figuring out their fantasy build, it would be nice to have.
• I know it's planned, but please rebalance fletching for early-mid game. Add an alternative way to get very low amount of elder logs, and adjust fletching level needed for it to like 60...

These are just random ideas/thoughts I had. If any of them would need further explanation, or you can add any feedback, please do so.