Currently, a 3D model is built from sketches and features. In these sketches and features model dimensions are often present. In general, these model dimensions are driving dimensions, meaning that changing such a dimension will alter the model. Furthermore, a model dimension can be provided with a tolerance. for example 30H7 or 40+0.2/+0.1, etc. 

If you want to use SW MBD, the next step is to provide the model with MBD annotations (Size & Location dimensions, GD&T, notes, etc). The issue that I have is that the MBD Size & Location dimensions cannot be linked to model dimensions. Moreover, the MBD dimensions are always driven dimensions, meaning that you cannot change your model by changing these dimensions.

The idea.
An option that allows you to link an MBD dimension with a corresponding model dimension, thereby fusing both the driving model dimension with the driven MBD dimension, creating one single MBD/ model dimension which is driving. 

How could this work?
Let's say I have a sketch dimension of 30mm. and I have an MBD dimension which is also 30mm. I then right-click the MBD dimension and an option appears: "fuse with model dimension" then a pop-up window appears in which I have to choose the model dimension. For example "D1@Sketch1". Then SW will test if these dimensions can be linked to each other. This can be done by checking if both dimensions respond the same. For example, change the model dimensions from 30 to 30.0001. And if the MBD dimension is now also 30.0001 then the dimensions are referring to the same thing. So they can be fused.