Reading this long and quite fascinating thread, it seems there's at least some general consensus that WotC could win back quite a few lapsed customers by doing at least one of:
4. supporting older editions in DDI, Dungeon, etc.[/list]
I can think of absolutely no good reason why they don't do #4 right now. As has been pointed out elsewhere, the cost of doing so would doubtless be covered and then some by the increase in subscription revenue, and assuming said support was generally any good the increase in goodwill value would be tremendous.
Let's say that Wizards include one previous edition adventure in each month of Dungeon Magazine. Month one, OD&D, Month two, AD&D, Month three, AD&D2, Month four 3.5e, then repeat.
Is that worth your money? $10 each month for just those adventures?
I would suggest that most people wouldn't consider it worth it. And the "goodwill" you create by publishing those adventures is nice, but unfortunately you lose the goodwill of the 4E customers who are losing the 4E content you sacrifice to put in the older edition material.
Splitting the market is such a major thing to RPG publishers and players because RPGs are so time-intensive. I have over 200 boardgames, but each weekend I'm likely to play 5-10 different games. In a year, I'd be lucky to play three different RPGs. I do not believe that RPG players in general and D&D players in particular tend to hop from RPG to RPG.
The making available of previous edition PDFs is another matter entirely.
Cheers!