Now, all that said, it is entirely possible that I'm wrong. Maybe there is a big demand out there, maybe large numbers of people are eagerly dreaming of 'official' support of their edition of choice. My gut says, no... but I have been known to be wrong.
If I were WotC, and I were considering something like this as a direction going forward, here is what I would do: Produce a single,
new adventure module for 1st Edition.
The other thing that they probably should do is get those old edition PDFs up on DDI in some form. That would seem to be a pretty cheap thing to do (although some will need rescanned, and they'll need to do something about DRM/format/whatever), and it would probably bring in a bunch of new subscribers.
(Oh, and incidentally - everything I said about old-edition fans not watching what WotC are doing applies equally to 5e. If they're banking on 5e pulling back huge numbers of 1st Ed fans, I fear they're going to be disappointed - if neither of WotC's previous editions provoked you to upgrade, why would you even look at their new attempt?