A typical modern router has at least two radios, 2.4 GHz and 5 GHz - 6 GHz soon to follow (already existing, but still very high-end, read expensive). With IoT devices still being largely 2.4 GHz only, providing 5 GHz only AP services might not be overly useful.
With DBDC one (modern-) card can do this (and some mt79xx cards fall into this category), but at the expense of its abilities to use all rx-/tx- chains (making two 2x2 cards out of one 4x4 card) and affecting its abilities to do Mu-MIMO and beamforming. So yes, this can 'work', but at the expense of the expected performance values of "802.11ax".