(caution, I believe there is an F-bomb somewhere in this video :)
This tractor-style setup was designed for California Quail, which as native to North America and have only been kept in captivity for the past 50 years or so. As a result they are still quite flighty and wild and due to their nature need a lot more space, vertical flying area, perches, etc. than the well-domesticated coturnix. This video gives you a good idea just how different Californias are - Gambel's quail, scaled quail, mountain quail, montezuma quail and to a lesser extent bobwhite quail are all similar in this regard. Bobwhites are more intensely bred in agriculture and have adjusted to life in captivity a lot more than the other species listed.
This setup would also be fantastic for coturnix or for a couple of small bantam chickens like Belgian d'Uccles, old English game hens, etc. In a ground pen one cannot stock the pen with as many individuals as with a wire-bottomed pen for sanitation reasons, though. This pen is 12 feet by 3 feet (36 sqaure feet) so one should easily fit 36 coturnix and in a pinch up to double that number if the pen had a wire floor. Also, with a wire floor one could prop this cage up to waist level so the caretaker didn't have to bend to get into it. California quail are not birds that are easily handled, so in this scenario the only reasons to go in the cage at all is to top up feed and water. In a coturnix cage where the birds tend to only use nest boxes 75% of the time, you have to go easter egg hunting every day. Californias tend to lay a couple clutches of eggs per year where as coturnix lay all year long.
To make this setup ideal for a few pet coturnix (say, a dozen birds) would be easy and the birds would have a fantastic home. I would either put a wire floor on it and raise it up 3 feet off the ground, or put a plywood floor on it and make it so that the whole side of the cage can come off for cleaning the bedding (a layer of wood shavings). Another option is to make it 6 feet tall so a person can walk right in (it wouldn't benefit the birds much as coturnix rarely fly and don't utilize vertical space very much - mostly just for a human's benefit to have it taller!).
There are as many different setups out there as there are quail keepers - I thought this was a great example.