scout is a concept, not a specific set of features. cooper advocated the 308 but look at what he was working with at the time. there are a lot of cartridges introduced in recent years that can do the same thing 308 can, but better. had he been alive today do you think cooper would watch a 308, 7mm-08, and 260 remington performing side by side and still pick 308 as his cartridge of choice.
one of the most amazing scout guns I've ever seen was built off a swedish mauser action in it's original 6.5x55mm and I would sooner own that than any 308 chambered scout gun currently offered for the simple reason that 6.5s in general have much better ballistic coefficients and can easily kill anything in these united states short of bison and even those would not be outside the realm of a well constructed bullet in the hands of a skilled marksman at a decent range.
in the last couple years I have become a huge proponent of 6.5s especially 6.5 grendel for it's compact nature and 6.5 creedmore for it's long range capabilities. they give the best combination of flat trajectories and retained energy which 30 calibers and 22 calibers just can not pull off. are they a compromise? possibly but everything about the scout concept is compromise.
zoomed optics, but only a little zoom(4x is the most common I've seen)
strong cartridge, but can't be too heavy
lightweight, but must also be accurate
must be able to shoot long, medium, or short ranges equally well which means that it's not going to do all ranges superbly as a purposebuilt rifle would
and it must be able to kill any animal up to 400 pounds at any range that the shooter would be capable of making a clean hit to the kill zone...
...ok maybe that's a little beyond 223 for most people but there have been a few cases of people getting lucky and killing elk with 223 and up in the great white north they've been using 223 to kill polarbears(way more than 400 pounds) for years.
that's just my take. if you are a good marksman and you are using the best ammo that 223 can offer I don't see why jeff cooper would not be impressed with a scout rifle chambered in that round.