Yes, I think the competition for them has risen as the free products have matured into pretty good VTTs. Makes me wonder if they wouldn't be better to simply publish a polished framework for something like Maptools.
I agree that this would be the smart way to go but there are some issues;
1) the VTTs I have looked at have been implemented in Java or Python.
2) WoTC have made a decision to go with .NET and I suspect that there is a corporate policy to go with Microsoft product and that it is made at a non technical level so difficult or impossible to change in the short term.
3) That all the bits integrate. That is, the Monster builder, encounter and campaign manager, mapper and VTT are integrated suite.
Now having said that, If I were in charge I would buy Masterplan (I have not tried myself but I have heard good things about and it is in .Net. So I would pay the developer to change the GUI to match the Adventure Tools look and feel and a plugin interface to implement so that the Adventure Tools can talk to and manage the Masterplan components.
Then, I would buy a Python based VTT, assuming that there is no good .Net one out there. There might be, I have not found one but then I have not looked that hard.
So, why Python? well there are good Python implementations that are integrated with .NET and that should facilitate creation of the necessary components to allow the VTT to integrate with the rest of the Suite and the Character Builder. It is also less for the WoTC developers to learn since they can use their existing tools and can do the bulk of the work in the language they are most familar with, make used of interfaces and plugins to connect the bits together.
Once they have a working integrated suite then they can port the VTT over to native .NET languages, if they want to.
What are the potential pitfalls? Well there are a few. I suspect that originally WoTC viewed the VTT and its integration in to the other tools as a product that they can charge a premium for. If they buy in that could be an issue with the fans since there would be an undoubted preception that WoTC is taking something that was free and now charging for it. As well as removing the perviously free content.
Some of the free VTTs are open source and the developers might not sell for any price.
So what could WoTC do then, well I think that they should monetise it in a different way.
Exploit the open source nature of these developements and fork one of the existing VTTs by creating a framework that connects it to the rest of the suite but that only works with an existing DDI account and uses web services to pull information from other WoTC applications. It means that you need an active connection to import encounter data in to the VTT.
Then add additional services that would be premium content like by appointment but nearly always avialable LFR sessions or encounter sessions or stuff like that.
Another thing that has occured to me, now while I have had a look at a couple of the free VTTs I have not really used one in anger but the ones I have seen use tokens to show the locations of players, monsters etc. WoTC demos of their planned VTT showed 3d virtual minis, so that could be an issue also. They may feel obliged to deliver that also.
Just my 2cents.