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Mostly that the big advantage of 68mm shells in the potential for low Q
The big advantage for me in using 68mm shells is that all the cranks I've got will fit in 68mm shells, whereas only some of them will fit in 68mm BSC shells with BSA30/386EVO bottom brackets. The Specialized FACT cranks, for example, which I'm rather fond of.
For a standard road double chainline, I haven't found using 135mm rear hubs to be an issue. I appreciate it might be if you insist on running small/small combos on bikes with ultra-short chainstays, but since I do neither I've not found it an issue so far.
Brommers-
For a standard road double chainline, I haven't found using 135mm rear hubs to be an issue
It isn't as long as your Q is about 145mm for cranks of conventional thickness. Since 145mm Q is readily achieved with an 86mm BB spindle, the direction of travel for road bikes is naturally towards wide BB shells, as they provide a good foundation for all the other tubes running into that junction.
gbj_tester
Mostly that the big advantage of 68mm shells in the potential for low Q, and you can't exploit that as long as the rear end is as wide as it is, and getting wider. For 135/142mm wide dérailleur rear ends, 86mm is narrow enough at the BB shell for the chain run to the top sprocket to be the Q-limiting factor, and you can use 86mm×30mm BB axles in a 68mm BSC shell.