I just finished Victor Vran and got couple of nice idea from that game. I didnt grind toward 100% since I rather finish other game instead (really wish have time for it).
1. Gamepad support
Probably not doable without proper input hook and it hard to code for online purpose. The game play nicely with controller with dedicated dodge, weapon switching and jump. Additionally it have auto-aim so wouldnt struggle much to get precise aiming. I tried to do it in median myself, but aiming skill is kinda tricky.
2. Toggle-able difficulty / reward
VV have 5 type hexes which add slight difficulty for player, in return reward player with magic find and exp gain. Median used to have this feature in past called Hard Mode Charm. I believe it was removed because player can abuse it by become hostile with each other since the item grant aura that give bonus stats to hostile.
3. Map Challenges
VV have various map challenges that play around with activating specific hexes combination. Some of them are time-based which required player to kill specific amount of enemy while the hexes on from the start of the game (can reset map in game). Additional other type of challenges are including "killing monster with specific weapon", "killing specific amount of enemies without taking damage", "destroy specific objects" etc
4. Weapon switching and Playstyle
The game doesnt have skill tree like in normal ARPG, so it designed to play around with "suits/armor" and weapons setup (think like dark souls / bloodborne with specific weapon animation). This probably not doable in sigma, but I really wish there are a specific gear that can be powerful but have negative effect that player will switch around depending on their build (like most new chaos RW). Median have weapon switching, but most people used it as pre-buff gear (shamanka on switch) rather than using 2 weapons that different purpose for different encounter
5. Cards / Charm with limited resource
One of median "problems" was bloated amount of charms which seem like the only way to progress in end game. In VV, the destiny cards function are kinda like change-able passive with limited (5 max) slots and you have very limited amount of destiny points. You wouldnt able to wear all powerful cards since it have it own cost and some of unique cards are only allowed 1 in the deck. This feature is the similar one in the game Paladins. Additionally, these cards can be upgraded multiple times and it also have branching part for upgrades like divine (random defensive bonus) and wicked (random offensive bonus)
6. Upgrade ingredient
4 Main ingredient for transmuting in that game are weapons, demon power, destiny cards and power stone. When you want to upgrade specific gear's stats (think like upgrade to max of affix range or new tier affix), you will required tons of specific combination of ingredient. Basically it made your gear not exactly useless since you can cascade upgrade them until you have perfect gear. Upgrading to new tier however, still required some luck though. Basically, if we implement in sigma, it more about collecting specific type of gear with correct rarity to upgrade your gear rather than buying it from vendor.
There are probably more stuff I forgot and didnt managed to explore since I immediately uninstalled it after finished the games.
Thank you for reading.