Is this an unauthenticated mesh? Ie. might my neighbours device be forwarding data for my device and vice versa?
By allowing 'unauthenticated' meshing, the total radio throughput in a typical urban environment is dramatically increased. By 2x or more often. Typical packets will take more hops at much reduced transmit powers each time.
The main reason not to do so is "what if my neighbour has crappy devices and black holes all my packets".
But your neighbour can already jam the whole spectrum and block all your packets. We design devices to meet specifications for a reason - and if the spec says "you must forward all packets according to this spec", and you mod your device to blackhole your neighbours packets, then the FCC will consider that jamming and treat it the same.
So... they'll do nothing?
But companies will be scared into only releasing devices that meet the spec if there is a decent risk that non-spec compliance leads to the whole company having their imports blocked.
Besides, forwarding packets for another wifi user will likely all be handled in the wifi chipset, so there will probably only be ~10 implementations by the ~10 companies worldwide who design wifi silicon. And if you're splashing out tens of millions of dollars on a wifi silicon design, you probably are going to make some effort to getting it sufficiently spec compliant to not be banned.