Except that these barriers are all really nothing more than a chicken-and-egg problem. Nobody builds a phone that can do all the HSDPA bands, but that's not because it's hard. The only customers who care about the 1700 MHz band are in the U.S. and Canada on carriers that don't sell unlocked phones, and there are no laws requiring unlocking. As a result, those customers don't expect to be able to move from one carrier to another without unlocking. As a result, the handset manufacturers don't need to build phones that allow this. As a result, the chipset vendors largely haven't bothered to design the chips to make this possible.
If you can build a 5-band handset, a 6-band handset is really only incrementally harder. Even a 12-band handset is only incrementally harder when you factor in electronically tunable antennas into the mix.
N8 supports the following bands: