Two UUs would favour a Civ with a strong expansion and military focus. Traditionally in the series those are the Greeks, Romans, Germans, Mongols, Ottomans, Aztec or Zulu. The Zulu don't really have much to offer in the UU field apart from the Impi. So it's not them. The Aztec while warmongers can offer more interesting options in the UB/UI area. The Germans already began migrating towards a more economic focus in BNW. Doubt they will go back to the military focus. The Greeks will probably get some other specialization this time. Especially if Firaxis decides to replace Alexander with somebody else and since Greece offer more interesting design choices than just being another warmonger. That leaves us with the Mongols, Romans and Ottomans as the likeliest two UU civilizations. Of course point could be made that these three civs could easily work with only one UU or have a non-militaristic focus.