While I would love to say yes and that it's technologically feasible and likely to happen, I would bet against it.
Past demos on older hardware do not mean much of anything going forward as the early Continuum demo on the 1520 demonstrates.
Also, given Microsoft's abandonment of most of the remaining Windows 10 Mobile phones with the Creator's Update (and past behavior) does not make me confident that doing what is "possible" is a priority.
(The Snapdragon 800 in the 930 is certainly more powerful than the 400 in the 640 but nope! 830 with identical specs and chipset as the 640? Nope!)
Now if they came out and explicitly announced that existing hardware like the 4s would be getting this new functionality, I would still wait until it's out on production phones before believing it.
(MS still sold BLU Win Jr phones in stores/online, labeled as getting the Windows 10 Mobile upgrade both before AND for some time AFTER announcing that it will not.)
In short, I would not buy a Windows Phone, or any phone in fact, based on the prospect of future features.