DrNoun

If you are logged in the website, there should be an option to send a mail like ingame (basically /mail send, but in the website), and its linked to the server one, so if i send a mail to someone from the website, he should be able to /mail read ingame, and same for ingame --> website.

1.15.2 has many good new features and shulker boxes. If you don't want to update because of PvP, you could make/get a plugin for 1.8 pvp in 1.15.2. And if you don't want to update, you could add shulker boxes as terracota or as backpacks like in RPG but in all gamemodes.

Selling ranks that can get OP kits is against minecraft's EULA, but it is allowed to sell cosmetics. You can keep the kits possible to get, by buying them in /shop.

Adding UHC to ec would be a great addition. UHC is basically survival with rounds. (solo or teams). First, PVP is disabled, but in like 10-30 mins, its enabled. And the border shrinks slowly.