We should have already been able to do this.
$ony wants us to pay for that gaikai.
Not to mention, we'd have to wait for them to add games to it.
If ps/ps2 classics is any indicator to how swell that process(gaikai adding games) will be, then I don't expect much from said feature.
Oh but you and everyone else would have thrown a fit if they included a chip in that allowed backwards compatibility and drove up the price of the PS4 to $600 again like what happened with the OG fat 60GB PS3 that had the emotion engine backwards compatibility chip.