Will there ever be another huge MMORPG?

Will there ever be a real successor to wow?

Titan was something of its own and, according to my information, had nothing to do with WoW.

It depends on how you define WoW 2.0.
A completely new WoW, where everyone has to start from scratch and which is based on a completely new engine, will certainly not exist.
That would put off the current players, because almost everyone has put hundreds, thousands of hours of playing time into their account and their associated items, titles, mounts, pets, achievements, etc. If all of this works, they will feel completely screwed up and almost certainly not play any more. Personally, I am not one of them, but I know enough people who do.

Especially since you would simply “throw away” the current WoW over 20 years of development time / costs.

I would find a kind of new look for the current WoW much more logical and sensible. As you have already written, WoW is now really old and nowhere near up to date. However, WoW has its very own, almost timeless art style as known from e.g. Okami or The Legend of Zelda Windwaker.
As a consumer, I see major problems in performance. Nowadays, WoW can no longer be played on every device despite the “simple graphics”. I know that from my own expirience. A gaming computer from 2008, for example, can just play the game at levels 1-3 out of 10 and you don't even have 30 FPS continuously. And even my laptop from 2015 only managed the game to medium to high - raids were unplayable in Legion.
With current high-end systems, things are going great! However, I keep noticing that the particle density causes problems. With certain effects, there are frame drops down to the single-digit range.

As some have mentioned, the cost would likely be too high. Anyway, the MMO market has changed a lot since the release of WoW. After all, WoW has been on the market for over 15 years. Younger players in particular prefer to play fast-paced players such as League of Legends, PUBG, Fortnite and Co.

This has once again become a wall of text. Sorry