There are several advantages to internal routing, additional design flexibility with asymmetric designs, etc, which makes T47 attractive. I think the benefits created by having a larger tube are mainly limited to the construction of metal frames and lugged carbon, which is where the T47 originated. It's just a threaded version of PF30.
IME, the bearing size stuff is marginal to the point of being nonsense if the bearing is well sealed. Most people in shops seem to believe that SRAM-branded dub BBs have great longevity, and those that use tiny bearings. Those opposed either claim that they are wearing through a lot of BBs, regardless of size (i.e., something is wrong with the bike or the installer), or are just discussing theory. Long-winded way of saying that the BB standard used wouldn't prevent me from buying a frame.
That said, if you made me king for a day, I would decree that all bikes use T47 or some variant thereof to get us down to 2 types of cups, 1 standard bearing size, and a bunch of reducers. I am not really opposed to BSA either, but realistically, the weight difference is marginal. It's around 20g in a carbon frame, including the BB, and about 50g on a Ti frame.
This XMcarbonspeed frame looks excellent IMO. Geo isn't my cup of tea; nevertheless, I'm looking forward to seeing it built up.
