Imo, there should be more items, and they should be more specialized.
Items serve two purposes in this game, to amplify a champion's overall power and allow them to scale (statstick items like Infinity Edge) or provide interesting utilities unique for a situation (Zz'Rot Portal Siege or massively improving your defense at the cost of offense). Currently, we have way too many items serving double time, providing wonderful stats for their respective users while also providing ridiculous passive effects. Need look no further than AD/C itemization to find items with wonderful stats AND passives.
An honest review of each item in the game, which items are supposed to be niche and which items are supposed to be generalist, and then breaking down these items based on their function or possible functions (creating multiple items out of say, Death's Dance) is what we need right now. As well as that, the inclusion of new items to fill in niches are design vacuums that drastically need addressing. Lethality is cool and all but super limited. Crit itemization is facing a lot of issues thanks to its mix of Passives and stat lines. Mage Itemization has been in the shitter for forever. Etc. etc.