This feature, available in some form because of the multiple radios, will be improved upon with t he introduction of VOLTE( voice over LTE) which is why this is being touted as a big deal. Though most LTE phones can currently do voice and data a the same time because of the separate radios, having one radio that can do both, similar to GSM phones is what VOLTE will allow but with a much better throughput. being able to do SVLTE is a necessity of being able to use VOLTE which is being tested and expected become widespread.
basically they are future proofing the phone.