It's so disappointing to think that they're 30 years behind, but not surprising. Part ownership isn't the same as practicing law, and a firm could possibly be structured so that the legal decisions aren't made by non lawyers. I can see how this might get a bit ethically complicated, but it seems possible.
I would think a lot of the big clients that firms compete for are multinational corporations, but sure, the U.S. market still matters. As far as the benefits of outside ownership are concerned, I think the article is saying that if law firms allowed the partners to have traditional equity like owners of other businesses, then 1) lawyers could devote more attention to long term business development, instead of being short sighted, and 2) there would be opportunities for financial innovation. At least that's what I took from it.