I believe that most of the feedback fitting with what I've been looking for has started to slow down, so I think I'm going to set a new closing date for this thread, tentatively set for the 30th. I have a LOT of stuff on my plate already, enough to keep me quite busy.
I've divided most of the feedback into 2 Phases; Phase 1 was an initial batch of things for me to get approved, so that I could begin working on them while additional feedback continued to accumulate for a "Phase 2" approval pass. Phase 1 has already gotten most of its approval/deny sign-offs already, and is well underway for implementation (over 100 changes are already approved).
Over the next week or so, I'll be compiling the remaining feedback into Phase 2 for processing, which will get another approve/deny sign-off from Red and Cenx, and then we will be implementing all of those changes.
I am open to the idea of sharing the upcoming decided changes AFTER they are all approved/implemented, because sometimes sitting down and actually evaluating a list of changes can shake some new perspectives free. However, I cannot promise this at this time, it will need to be approved by Red and Cenx. Furthermore, some changes are internal only and may not have permission to share even if the overarching list is shared. So that's something I'll be thinking about in the coming weeks as well. I may re-open the thread purely from a "evaluate the changes coming" approach.
Another possible option (and one that might be more within this update's more limited scope) is that, instead of re-adding the biome key molds, what if the keys just don't drop at all until Plantera has been defeated? And maybe their drop rates could be increased slightly to compensate for the new boss requirement.
I think this would be a poorly received change. The post-Plantera segment of the game moves fairly fast, with a lot less time spent in the matching biomes (Corrupt, Hallow, Ice, etc) than is spend in the earlier sections of Hardmode. Given that the Hardmode Dungeon chest items are generally powerful but NOT meant to be end-game viable, this would significantly limit their window of obtainment, even if we boosted the key drop rate.
I do not see re-implementing Keymolds being a thing we will be doing.