Everyone, please note that the original question was asked in April 2016, so we are nearly 6 years after the fact discussing it. So there really shouldn't be a "To get back to the original question" because it's not something that someone is trying to solve now...
The follow-up question of "Does something like this exist", the answer is clearly "no".
The further discussion of whether something like this could or should exist is potentially legitimate. It might have been better placed in its own thread though.
Something like this clearly could exist if it was attempted, and we know this because the file format for NXG most definitely was done this way. GVI files were XML and you could look in them. However, changes were hard to pry out of the file because it was littered with tons of unhelpful things among the things that were human-readable.
While it should be theoretically possible to write a script that traverses the entire front panel and block diagram of a VI, finds every object on them, and then reads out all of their properties, there are enough "under the hood" things that would make putting a VI together again exactly the same as it was before not realistically possible. NXG was able to do it because it was engineered that way, but I don't think anyone short of a very dedicated team of NI employees working on this for a long time could make it work perfectly.
I think the real answer to the root of the follow-up question here is that there isn't something like that, and probably won't ever be, but if your objective is truly to get a better way to use a source control solution designed for text files to work for LabVIEW files, I don't think it will happen. The two things you can realistically do now are to use the "Separate compiled code from source file" option on your files so that changes to other VIs are much less likely to cause ripple-effect recompiles to create false positives for code change, to be much better about documentation (in the VI itself, in the VI properties, in the VI history log, as well as in comments on source control commits), and to use the LVcompare tool when you still need to know more about what changed.
Traditional text-based comparison tools are basically 1-dimensional, comparing long text strings with each other. LabVIEW has additional dimensions to compare so it will never truly fit in.
