Once DDI is totally set up, then I will start thinking WOTC is seriously thinking of what to do next.
DDI makes it
less likely there will be a new edition, not
more likely.
For any 5e to succeed, it probably has to be significantly different from 4e. The motivation for a new edition
has to be to bring in new players, whether those are lapsed players, or those who rejected 4e for Pathfinder/3e/retro-clones/other games. However, the "Red Box" was targetted at truly lapsed players, and doesn't seem to have set the world alight. So, the target this time must be the Pathfinder/other crowd. And those are people who can be assumed to have looked at 4e, and decided against. So, something different is needed.
The problem is that a significantly-different 5e would render the existing DDI tools obselete. They would need thrown out and replaced, with very little reuse possible. (The VTT being an exception, but it's not yet released. Curious that that now seems to be the priority...)
What that means is that if WotC are planning a 5e, the best time to do so is
now, not after they've invested the monies required to 'complete' the DDI. That would just be a waste.
(The one exception to this is if they consider the DDI a failure, and are planning a 5e that simply does not include one. In which case, they may seek a way to exit the DDI strategy 'gracefully' - which might well suggest completing at least the Virtual Tabletop. However, I don't consider this very likely on two counts: Firstly, I'm pretty sure the DDI
isn't a failure, at least financially; secondly, I doubt WotC would care about a 'graceful' exit - summary cancellation would be more likely.)