The Custom Item Set Menu is Too Cluttered

There has been a creeping problem that needs to be addressed regarding Custom Item Sets. Ever since the introduction of some Featured Game Modes (ex. Nexus Siege, Nexus Blitz, Poro King, and Odyssey), FGM-specific items have started to clutter the menu. Without a filter to remove these items, these offending modes cover the menu with "duplicate items" and items that belong to modes that have long passed (Odyssey and other FGM's respectively.

Here is an example of the issue: https://gyazo.com/56df0fa8fedefe5cdb623a95b99c3513

These "duplicate items" (BoRK, Maw, BT, Mercurial Scimitar, Gunblade, Ravenous Hydra, Death's Dance, etc.) are not a menu bug, they are the "Space" item line (11) from the Odyssey game mode which have altered stats balanced for that mode. Since they've been added, placing the normal items in your set require double-checking or else you'll be stuck with an item that can't be used on the normal, permanent maps. Nexus Siege and Poro King are also guilty of having items that clog the menu. On top of that, modes like Odyssey and Nexus Siege (not Nexus Blitz) are not intended by Riot to become permanent modes; rendering Item Sets for those modes redundant since there is no clear rotation schedule for FGM's. For now, these items leave 18% of the item menu cluttered (47 items out of all 255). We have no convenient means of keeping the menu streamlined to formulate map-specific builds for our champions.

While I do acknowledge that most players do not use Item Sets, I think it would be nice to make it more pleasurable for the ones that do. Perhaps it would be best if Riot added a mode/map-specific filter button in the left column (ex. Non-FGM items only, Summoner's Rift items only) just like the item stat buttons? They could also delete items from modes that will not show for a while. This in turn could encourage new and veteran players to make Item Sets more often while making the experience less confusing and annoying.