Persistent World ideas are tricky things, and in this case, I must disagree again.

One thing that was slightly useful to me in the first place, and part of why I didn't raise a shit on the first suggestion of EH (though I never really supported it, either), is the fact it had structure. Everything was connected and could be connected, there were limits, there was a general thing going on. The suggestion is now literally what exists at the moment, because EH no longer has the structure. All the things you mention could be done with the current structure. While it may come out better if the entire PW forum was rewritten to make a clear indication (if that route was run through), that this is what the people there want.

But even if it is rewritten, I still would not be in favor. Because what you suggest is effectively what exists now, and I fundamentally disagree with a broad, unrestricted multiverse. It serves no purpose. In a sense, the current forums are [i]literally[/i] the same thing. If a couple GMs want to link and create a multiverse, they will do that. If they don't want people to interfere with their canon/multiverse, they can, and will do that too. If they want to make a true Persistant World, which is distinct from a multiverse, then the GMs can link their canons. None of that justifies the creation and maintenance of a unique forum.

I would instead consider it viable if the idea was approached with more unity and structure, not only in general rules and "what you do here might affect something elsewhere", but also in genre. A balance should be achieved. Yes, players need flexibility. That's the core of the idea. But it also requires structure and unity, not only in terms of timeline, but also in things like power level and technology (in my opinion and based on how the site works, especially the community base). A specific fantasy PW would make it easier to avoid a fairly average swordsmen being absolutely obliterated by a sci-fi grunt with a gun and heavy armor. It would make more consistency at large, making it easier for plots and characters to connect (in a way, like a roleplay MMO, only with more flexibility). It would allow easier maintenance and judgements as to what is too powerful and what is not, because you can look to fantasy stereotypes to make more balanced decisions when accepting characters and making judgements should a conflict arise (as compared to cowboi supagunslinger vs Archmage of Canterbury or something, and a drama potentially arising from that combination when the two entities meet). Repeat a similar philosophy with modern and sci-fi settings, and in the future, add more if there is enough popular demand. Finally, my main, short term revision idea would be to put the PW section in line with other sections so it does not somehow get standing over all the regular forums despite having an abysmally small fraction of the activity and relevance seen in the three sections below it. 

As it is now, and as the idea seems to propose, there's just not enough to bring things together. It becomes clutter that might as well go into the regular sections anyways.

It's not an easy overnight solution, but I think you're more likely to find the answer in structure and a degree of unity, not in making divided verses that don't even need to exist in the same forum.

And as for existing games, they would not have to be deleted. I believe they would work just fine dumped into the casual section, as they're largely independent entities anyways.

In short: Sure, have a multiverse. But it does not need its own forum. Not as it is described, and not as the EH operates right now.