Are you sure that data-models are covered by GPL, that was one question I really had. If they are then I think the whole point is moot. MS will re-engineer because they won't let GPL code into thier fold.
I thought that I read discussions to the effect that data-models are information and therefore exempt from copyright(left). Take for example, a schema person with firstname,lastname. If that data model is copyrightable then I will be first in line to file.
An analogy in the music business (which I am fully versed in copyright). You can't copyright titles and you can't copyright chord progressions. I think this would apply to this domain as well. If you can copyright data models we are all in violation as I am sure that someone did (amazon, MS,Sun).
Now the process of using those tables may be patentable, but I am not sure how copyright would work in the straight data model scenario. I am sure I can reverse engineer the data model of ACT and make my own with a different front end and they couldn't do anything about it. The same goes with Quicken and a lot of other programs.