I know that resale value concerns speak volume for a 2-sink configuration in the master bathroom, but I think it is a bit of a fad. Perhaps for my house it would be just as important to have two full master suites - "for the mature couple with separate sleeping quarters" as the ad might say ;-)
I bet a single, spectacular, very wide sink would distract from the lack of the obligatory 2 vessel sink configuration and end up looking much more generous and stylish.
I found some really nice and inexpensive ones in my Danish catalogs, as for instance:
My favorite (don't know the brand)

Intra Wing

Now to the usual problem: how to find something equivalent on the US product market?
Here are some candidates:
1. Duravit 049112, $1022:

2. Cantrio, $1553:
This one is 60" wide!3. Neptune form Ira Woods, $675 - 50" wide:
3. good ol' Starck, $712:
, a 41.25" wide sink