There's the matter of which technology to use for coding it. I'm doing web-dev in school with nodejs, so right now that's what I'm mostly acquainted with. I have a couple of web game projects that render stuff directly on the webpage using html canvases, and do multiplayer networking stuff via sockets. In theory it's possible to do it this way, but web+socket games are difficult to protect since front-end code is so freely available to the client.
Re-learning C++ is also a possibility but that'd be time and mind-consuming!
I've never done an isometric game before, but investigating a bit, it's not complicated to do. Fundamentally changes the rendering of map tiles, characters and such.
As for the game systems, animating the characters, linking the animations properly and moving them around sounds like a potential challenge, considering all the states a character can be in (rotating, moving, grabbing something, attacking, etc.) and how they should be able to change from one state to another seamlessly.
Pathfinding also sounds like a challenge. The obstacle map must be able to change dynamically considering all the moving characters. I've done A* before, and I'm sure it's reliable and efficient enough. Also to take into consideration is that characters need to rotate into the direction they're gonna move in before actually moving, so the character animation system should be reliable enough to support this.
The lighting/illumination system could also present complications, considering multiple moving light sources. I've dealt with this problem on a past project of mine, but I don't think it was particularly efficient, I'd have to check it again.
As for NPC AI, I'd probably just *borrow* code from the original v2 server, maybe changing anything that would seem reasonable to.
I've started a little nodejs project where I render some isometric tiles, walls and foreground objects in the proper order and position.
[spoil]

Potential improvements/changes over original v2?
Considering this would be more of an open-source hobby/side-project, not much attention would go towards server hosting, account safety and such.
This is more of a rambling thread where I throw ideas out in the open, motivation comes and goes, and I'd find it difficult to ever finish this, let alone progress to a playable state, but it'd make for a cool project to learn more from.