Global categories for Marketpress

It would be useful if we had an option to set global categories in MarketPress.

My argument for this:
We are in the early setup phase right now and I discovered that some of our sellers have created some rather interesting, but rather useless categories for their products. It is so bad that using the [mp_global_categories_list] is almost an embarrassment. Educating the sellers and convincing them to use standardized categories would be a feat unto itself.

While not everyone will have a need for restricted global categories, many of us are working niche sites in which categories or products are well established and being able to select, "Use global categories" would be a useful feature.

I think this is something that should be a core option for MarketPress. The individual sellers can already do it, but being able to establish them network wide would be great.