It seems to me that could work quite well. Basically, then, you would choose an MMP system. I think it would be desirable for the whole country, basically, to have the same system, not to have MMP for parts and STV, for instance, for another part of the country.
With MMP, of course, you will still always have the single-member districts. Both in the case of Germany and New Zealand, and I guess Wales and Scotland as well, they use FPTP in that single-member district and then proportional representation, which is a top-up, to make sure that the outcome is proportional. It seems to me that could work well.
Perhaps I could add a quick comment about the problem with MMP that many people have argued, the problem of having two classes of representatives. I think when one talks about electoral reform, it is important to realize that there is no perfect system; there's always a compromise that is necessary. The compromise with MMP is that people still want single-member districts. If you want that and you also want proportional representation, then MMP is the answer; then a consequence is that you have two different members of Parliament.
Compromises always involve things that may not be ideal, but in this case it may be a compromise that comes as close to the ideal as possible.