All else being equal, I'm not thinking about changing to 5E from what I've seen in these early play-tests. 4E is just too good.
Losing DDI would be a big black mark against my continued support, though. It's just gotten too good, too convenient. Like everyone else, I have limited prep time, and taking away my digital tools would mean the quality of my game would suffer (I'd likely have to switch exclusively back to pre-generated material whereas now I can just about run a home-brew with the time I have).
The only business case I can think of for hitting the OFF button on 4E subscription income is the damage "4E" might have on the next edition's brand, especially if they decide to just call it "D&D". Maintaining the database and the application servers is a real cost likely in region of thousands of dollars per month, but it wouldn't take many subscribers to offset that and I would imagine at least some of the fixed costs could be shared with the 5E digital offering when it arrives as well.
I suppose you'd also run the risk of ticking off those 5E fans who, if the DDI subscription also included access to the 4E tools, would start to complain (loudly) about the fact that they're "subsidising" an obsolete edition, and why isn't there a lower subscription for those who don't want 4E? Petty, yes, but as a community we've shown we can be very petty indeed.
Still, this problem is, what, 18 months away?