a) we would like to see 802.11ah support in OpenWrt
b) but someone will have to do the necessary development work
b.1) first in the mainline kernel (nl80211(!) and regd(!), then drivers(!))
b.2) then in hostapd
b.3) then in OpenWrt (netifd, wpad)
With a) assumed to be positive (after all that part is just wishful thinking), the question is all about b) - and that's firmly in the negative for every (sub-)point. The kernel doesn't know anything at all about 802.11ah, it doesn't know what to do with the frequencies, the channels, it has no regulatory information about them and there are no drivers (which covers everything of b.1)). Without b.1) anywhere (at all), there's no point thinking about b.2) - and without b.1) and b.2) completed, there's no point even talking about OpenWrt.
…or, as rightly phrased, "it does not work" - and it will never work, until the chipset manufacturer works on mainlining their drivers (and for that to happen, they will have to extend nl80211 before and get those changes approved/ merged). As none of the 802.11ah vendors have bothered about this yet, nor (apparently) even started discussions with the kernel's mac80211 maintainers yet, I wouldn't expect that to happen, probably ever. With the changes involved, I would expect the nl80211 side changes to require considerable discussion and review, before the driver changes are even up for review.
It's 'possible', but the proponents don't seem to care - so chances are nil, until that changes fundamentally. If the manufacturers were heavily motivated and invested, this would easily take 1-2 years to (potential) completion (really, if $vendor wants to introduce new features (in the scale of new standards with larger stack changes), get involved while it's still in the whiteboard phase of the standard, long before initial tapeout) - if they're good, they'll have their ducks in a row by the time their hardware starts shipping - if they neglect this, they're going nowhere fast.