One thing that is an absolute reality for firms doing software development (in house or for commercial sale) is that they more than like got a number of existing systems to support their activities. Rip and replace is generally not an attractive scenario, no matter how appealing a move to TFS might be.

The product group is working hard on a toolkit to aid in the creation of migration tools, that will abstract away the TFS object model and provide a plug-in architecture for building migration scenarios.

Link to TFS Migration Blog : TFS Migration Toolkit