I've traditionally argued against WotC taking all their old material and creating PDFs of them to then sell to people, because I've believed that if there was a true, sustainable and profitable market for them, they would have done it already. Basically, I've always argued that the people working at WotC weren't complete idiots, despite so many other people saying otherwise.
However, now with the idea of 5E and the possibility of newer gamer not only learning about the "older games" but in many ways getting to actually experience them within the 5E rules (plus all the old schoolers possibly transitioning to the new game themselves if it suits their fancy)... coupled with the idea of making a subscription to DDI the gateway to acquire those PDFs... I've come to believe that the market might open up enough and the profits from all the new DDI subscriptions profitable enough to make the PDFs of old edition material possibly worthwhile and useful.