There's no chance of a petition of this sort stopping WotC from working on 5e, no matter how many signatures it gets. The time for that was about two years ago.
In any event, I couldn't support it. I want 5e. And in time I'll want 6e, and 7e, and... Simply put, none of the existing editions leaves me completely satisfied, and there's virtually no chance of 5e achieving that either. So, keep trying new things, and hopefully we'll get there some day.
As for supporting all the old editions...
In principle, that is indeed something I would like to see. After all, why would I want them to not support other people? That's just mean.
Unfortunately, though, that only works if you have sufficient resources to support multiple editions and you don't care how many units of each you sell. But neither of these is true.
Each time WotC devotes resources to edition X, that means less support for edition Y. The reduced release schedule of the past couple of years hasn't been because they've just been sitting around - 4e support has suffered because of the work being done on 5e. Now, split that 5+ ways to support all the editions, and you'll be lucky to get one book for any given edition in the year.
Meanwhile, whether we like it or not, WotC have expectations over how D&D will perform. And that means that every book must justify its existence, or it doesn't get published. If they try to sell to a fractured market, then every book will sell fewer units than it otherwise would. And so, instead of one book doing well enough, you have 5 books which each individually fail. (And that applies even if the total sales of all together are higher, even much higher, than for the one.)
Now, that said, there are a few things they probably can do:
- Edition neutral products. Traditionally, these have actually sold quite poorly, but they may be able to get some of them to fly, especially setting-specific products such as "Menzoberranzan".
- Multi-edition products. Again, attempts by publishers to dual-stat products have usually failed, because it increases the cost to include the material, and every customer will then be paying for something they know they don't want. However, if they create something reasonably crunch-lite, it might be worth providing multiple sets of stats.
- Online conversion guides, available through DDI. Especially for 4e support (where the DDI customer base already exists) this may well be a worthwhile option.
- Opportunistic support. Maybe they do an article here and there in the e-mags (again, this is best for 4e, but that might change if DDI takeup amongst other edition fans increases). Or their "Free RPG" adventure could be 1st Edition, just for the nostalgia. Or something.
- Reprints. To be honest, I don't expect a lot of these, since most things are available via eBay for good prices, and very few items outside the core will be able to justify the costs even of doing the reprint. Still, they might manage a "Rules Cyclopedia", a new printing of the old "Red Box", or perhaps compilations of the classic modules (or even "Dragonlance").
- PDFs/PoD. I don't expect a great deal here, since the old PDF files weren't really very good in most cases, but anything that they do reprint should then be suitable for sale in PDF form, or on a PoD basis.
- Third-party support. I'm inclined to think that WotC would do well to formally open up the old-edition rules via the OGL. After all, the retroclones already exist, and already make third-party support possible, so it's not like WotC would actually be losing anything, but they'd get the goodwill of acknowledging "hey, we can't support this as fully as we like - you go ahead." And while we're at it, allowing support of 4e would be no bad thing, too.
