TLDR: Block that can make chests appear with a cool animation or other ideas that are more adventure-y in nature than the usual stuff in mods (not that they are bad, it's just different). For role play or quests or things.
The idea for this mod is that there are chests that are unique or interesting looking or appear in an interesting way. Useful for adventure maps, mods with questlines, or role play. It is possible some mods have these in them that I didnt know about, but I don't think there is a mod out there like this right now. To illustrate my ideas, I may reference something for another game to describe my ideas.
Also, since it is just a suggestion, I think the person making it could add whatever wierd or interesting features they would want to see.
These chests appear with a special animation in different ways when a certain block is activated.
Maybe the block would indicate where the thing appeats/vanishes from? Having some sort of interface to indicate where the chest goes and how it gets there.
<Currently Unnamed Chest placing Block>: Kind of like a command block but contains all the mod options for spawning in chests with special animations when they appear. Activated by redstone or by player?
Falling Chest: Falls from somewhere above until it lands at the spot. Maybe it becomes less transparent as it falls before becoming normal looking when it's in place? (Like some chests From the Zelda 64 games)
Light chest: Appears in collomb of light similar to how some special chests do In Zelda Wind Waker.
Illusion Chest: Appears with a wavy effect like some chests in Zelda the Wind Waker. (See the Lighting the Windfall island lighthouse for an example)
Darkness Chest: Appears out of a pool of shadow (See Paper Mario the Thousand Year Door, Riddle Tower for an example)
Water Chest: Like above, except it's a pool of water that freezes into an ice chest.
Fire Chest: Flames rise up, and when they lower a chest is there.
Require specific keys to open, maybe one of them has to be built from different key parts, or by inserting a gemstone into it? I know some mods probably already have this in use.
---Problematic Chests: These chests are dangerous and can pose a problem if opened.
Protected Chest: Won't open if enemies are nearby.
Trap Chest: Unlike the Vanilla Trapped Chest, This chest itself is a trap. Will it explode into potion effects? Freeze the player in ice for a bit? Explode into monsters? Shoot arrows at the player?
Hungry Chest: Blocks the way until the proper item is placed inside.
Chests that do something when opened? A chest that you open and it plays the animation and disapears, spraying items out of it? Maybe one that shoots out a fireworks. Something covered with vines that needs shears or fire to open?
Honestly, I have no idea how to pull some of this stuff off. Some of it could be done with Command block trickery, however I think there is some cool stuff some people could do that would only be possible with this mod.