balmy kite
The problem: After so many years, there are a ton of great items that are essentially dead content, because while they may have many cool features or abilities, they are too low level and are at best, a temporary upgrade. Which can still be not worth getting, as you can quickly out level the areas where those items would be useful.
The solution: A new skill that would allow you to upgrade these items to the next tier level, letting the player use them at any level, as long as they put in the work to upgrade the item (a bit like invention, but simpler and more accessible).
The benefits: A new skill, reviving over a decades worth of outdated items, and adding high level gear variety.
My idea: Let's call the items you can get from this skill "enhancers". You can create/obtain an enhancer for every 10 levels. Attaching an enhancer to a piece of gear will allow you to start upgrading it, and once you finish upgrading it, the gear will have the same stats as the next tier.
Example: Rune Armor is level 50, so lets say you attach a tier 5 enhancer to it, and go through the upgrade process. After upgrading, the Rune armor would have level 60 stats, the same as Dragon Armor. Then you could attach a tier 6 enhancer to the upgraded Rune armor, upgrade it again, and give it the stats of tier 70 armor, and so on. So you could even upgrade bronze armor to level 90, you would just have to upgrade each piece 8 times. The higher level the base item, the less you have to upgrade it to get to max level. This would bring items such as godswords, barrows armor, etc, not just to end game, but as sets players could keep as they level.
wary dagger
thorny minnow
shut geyser