Hi Lewanor, thank you so much for sharing your ideas and chronicling so much lore and information about a character that clearly means a lot to you. Your body of work is as impressive as it is staggering. As I hope you can appreciate, I don't have enough time to read through every facet of your work here. However, I found your gameplay kit proposal and would like to focus my feedback around that (especially since it's what I do at Riot!).
I really liked the emphasis on Talon's bladed cape, which I think is the coolest part about his visual design. I agree that there's a lot we could have done to push that idea further and make his cape more incorporated into his combat pattern. Maybe some of these ideas infringe too much on Irelia's identity, but I think the space is rich enough for two blade masters in one game. :)
As for removing his stealth on R and giving him some other tools, I think that change is a bit risky. You caught yourself by admitting that it may be too overloaded, and I agree with you. For an Ultimate, it's usually better to create 1-2 effects with obvious success/failure cases. Talon's current ult succeeds at this because it does the two things he wants most- deal a ton of damage to one isolated target and escape afterwards. By giving him damage reduction and slow reduction, I think he becomes less of an assassin and more of a skirmisher. Still a cool identity, but likely a different one from what Talon is today.