FWIW, even the sales people at AT&T and Verizon think that a key reason for sales improvements with the 7's were the return of micro sd slots. Samsungs's investment in 256GB mico sd fabrication should be proof enough. Phones are number one for micro sd attach rates and after market sales.
The development cost hurdle for Sandisk and Samsung to breach the previous ceiling of 200GB for microsd was costly to squeeze the extra 56GB in the current design that is compatible with current devices. Samsung would not have bothered if they were now not All-In for micro sd.