Im sorry, but it is Riot, and tribunal operated in a browser. As such there should be no technical problems that last for, how many years now? 2? 3? And these are not details, this is a big feature, especially in the community management, its not basic, and people should know if it is even being worked on,or is it yet another lie.
And yes, items giving exp may not be the right approach,but Riot should do something and notify of what they are planning, this is what transparency is.
And no, balancing out keystones would not be such a high impact thing,currently we have good keystones and bad ones, you can balance out the bad ones, even one keystone at a time if needed, so you would do it reguraly and without any chaos. This is not even near the level of class reworks, not even close.
No, those new gamemodes are different, with different items, rules and interactions even, if their sandbox is not going to be complex from the start, then it could have been done now, because the current client is enough for relatively complex functions that could be allowed to be edited.
Replay system is not even a feature now. And as such it could have been a feature outside of the client easily. It is better to have a feature than to not have it at all, just because of reasons that don't even matter to players. Who cares i replays will be in a browser or in client? What difference does it make? None.
And im sorry, but lore is ALREADY DISCONNECTED FROM THE CLIENT! Unless you want to tell me that 2 sentence bios are "connected lore". It is even hard to find previous lore. People needed threads for that shit! Yea, you need to actually deeply search for old lore!
It would take no resources at all, its just a link, and you wont read lore while playing a game, and the client is not that resource intensive unless you play on an actual toaster. But it would at least help a little, or at least would have helped.
When the new client would come, only 1 of these things would be needed to be redone, and that is gamemodes. The others things could exist easily or be incorporated in the new client with no difficulties.
Riot just chose not to do it.