What you just described was money walls, except the egg thing(not even, money walls had the precious resource emeralds at mid) and the thing about mobs getting harder with gen level, and the island. Still this game is 75% money walls. I would much rather money wall coming back due to how similar it is to your suggestion. Before you say it was not popular, it's because it was broken.
Okay wait a second all of these suggestions could be changed instantly
Instead of Iron, Gold, Diamond, and emerald
we can use redstone and coal to replace 2 of them
Also dude i haven't played money walls in like 4 months so i don't remember things clearly
Instead of mobs guarding the generators they could be stronger by not increasing their numbers BUT giving them better gear
The whole reason i added the egg thing at mid is to encourage players to go to mid than camp, and i remember money walls was just 1 big pvp area not islands, also eggwars has iron gold and diamonds and they also have enderpearls, some ideas came from the suggestions here and some were from OP mode in eggwars (Ender Pearl, Enchanted armor)
Strengthening the wither is something and so is covering it just like eggwars and money walls
Eggs Provide your wither with an extra bar of health (not from money walls)
Eggs Heal your wither (not from money walls)
Lost your wither = 1 life left (like eggwars and money walls)
And the Wither can be replaced with ANY MOB!
TBH Money walls had SO MANY similarities to eggwars, Diamonds turned into emeralds, Villager Shop, Covering your life source, they only changed minor features (Your life source has health bar, Mobs Guard generators, ETC) The only 2 BIG things they changed were their were not any islands but one big flat land, and walls were guarding and separated teams
This game i suggested has so much potential, many things here can be changed easily! if you have any problems with it just say it, but i want to say this
MONEY WALLS WON'T COME BACK no matter how much you wish for it, it will never come back, only if so many people wanted it back and the developers agree then it will so stop saying its too similar to money walls it is not, even if it is what is the problem with this similarity money walls isn't a game anymore do to the bugs in it.