After I watched a Wrath of Heroes video, I got reminded of all those small warfronts in mmos which were often just a grind for me. I don't see much long term time fun in that. Seeing mythic behind it, I couldn't stop remembering dark age of camelot and its old emain large scale RvR.  

Then I started wondering why there isn't a 100vs100vs100 moba with like keep/tower raiding out there yet. It would be like an instant 50 (max lvl) warfront with realm ranks (pvp ranks) restricted skills (for easier balancing), small mission objectives like taking towers or holding gates and big mission objectives like getting keeps. You could kill mobs for money to buy better keep raiding/defense items etc etc. Players would have the choice of going solo, random/premade groups or just zerg. In daoc there were always those three kind of players and not just one huge zerg absorbing all players from one realm. 

The zone / map has to be kind of huge of course, small and big mission objectives have to be far enough apart from each other so e.g. the smaller groups dont get in a fight with the bigger groups/zergs that are trying to take the big objectives. 

Upon account creation you have to chose a non-overpopulated realm, although I don't know about this point, because somehow a realm might get over-populated etc, so maybe you can just chose what realm whenever you want. Then again, you will most likely never feel a bond to any realm and it will just be team a / b / c.

So anyway, it was just a quick idea, tell me what you think about this. 

My first kneejerk reaction is that such a game which only focus on 100v100v100 MOBA RvR gameplay would be rather tedious and boring in a while, so I would want some side stuff to do like PvE mobs to upgrade keeps, maybe some random bosses, crafting, character progression, etc. And once you start adding those in, you suddenly have a MMO instead of MOBA. Which is what warhammer or at least Daoc did.

These kind of games don't really excist anymore, unless ya wanna play DAoC I s'pose.  The best PVP focused game that I enjoyed most was ShadowBane, personally I can't believe they scrapped that game, I think alot of people have said that was their favourite all time PVP game.  Basically, what I think is yeah, this kind of thing is a great idea but we've got it or had it and its dying out sadly, we need a game like ShadowBane back.

I like the idea. However it's a question of degree from moba to RTS eg Dawn Of Fantasy. But yes there definitely does seem space well below RTS (sheer size) and Moba mechanics to be bumped up in scale. Like it.

It might be just me, but I would never want a MOBA larger in scale than the frontrunners currently are. 5v5 for 30-45 minutes is right where that type of game belongs. With too many people, organization and communication become much more important than individual skill and then it doesn't feel like a MOBA anymore. And if it routinely drags on for more than an hour due to a gigantic map, that's no fun either.

The strengh of MOBA are balance and sorry large scale pvp is never really balance.

To answer your question GW2 has faction vs faction vs faction pvp that functions very close to what you are talking about