I just feel like, those letters do have some potential for events.
If we remove them from the Packets or wherever they drop from, and keep them exclusive for GM events or such, we could use them in a much more useful way.
For example:
There will be a list of letter combinations that you can collect, and depending on how many letters or which rarity the letters have.
There's gotta be like an item that only drops letters, and some are more rare than others.
There could a PVP/MVM Event and for each round a team wins they will get one "letter package".
Once someone gets a valid combination, it can be traded in for the corresponding reward on the list.
Letter rewards could work something like this:
P-K-O => Stack Rations
Z-A-N-K-Z-A => Great Fruit
X-Y-Z => ...?
I know this is not exactly Vanilla, however, the card system was in the original ToP, it was just never really used and I believe one of the letters (T, O, P) was unavailable in game or something.