(¿Reasonable?) Key Changes
Broken Key.
I think the broken key is fine as it is. Objectively, it is the weakest key although, at least to me.
A change I'd propose is to actually be able to find parts of the key, and turn it into a dull key. To do so you would have to search a minimum of two chests (there would be like a 15%/20%/25% chance to find a piece), complete the equivalent of 1 full generator, and save one survivor off of the hook. After getting the key pieces you can mend the key back to its original form by the means of a five second (if one-by-one) or twenty second action.
The generator progress would count for the new dull key's progress as well.
Dull Key.
There's almost zero difference in the dull key and the rainbow key as they function now aside from aura time and how long the hatch stays open. I think that could be changed.
A change I'd propose is that to activate the dull key's hatch opening ability you must have previously spent 80 seconds on a generator and finished one or been in chase for 80 seconds, with the key in your possession. If you give the key to another survivor they will have to fill the requirements for themselves. But the Dull key comes with one fatal flaw to differentiate it more from its better counterpart.
This version of the dull key will only open the hatch for one person. If you open the hatch, you will no longer immediately jump in unless you the original prompt instead of the new version. You are granted the ability to let someone else jump in at the cost of losing that chance to escape.
The hatch will stay open after the same amount of time as it currently does.
Rainbow key.
The rainbow key is objectively the best key out of them all.
The changes I'd propose are two gens times or 160 seconds of chase in order to be able to open the hatch. But it allows all survivors to escape from it in the time span of it being open.
Let me know what you think of these changes.