the food at nanban was horribly disappointing to me, went for the first time a couple of weeks ago.You'lll need to walk past quite a few places to get to said theatre if you're coming in by tube.
Either from top of Coldharbour or Atlantic road.
Some decent marketing and I can't see it being that difficult to get a pre-theatre crowd in for drinks or a two course meal for placees other than the Laundry. Yes - you won't get a much better location granted, but the options are bland and over priced. But with a little research before your trip you can certainly find better.
I expect somewhere like Nanban (just as an example) to do well when BH opens.