I don't think it has anything to do with the ever shrinking traditional futures/options pie. If I had to guess, I'd say they're trying to get into the OTC derivatives/repo clearing in Europe early. This might turn out to be a lucrative business and in Europe it's currently dominated by one large participant. CME is just trying to expand their presence in that space into Europe. I imagine all the FX futures talk is nothing more than an excuse to establish a foothold.