16ga has never gone away ....and for the last 30yrs ...Browning has offered a 16ga in their BPS Hunter ....and most years it was available in their O/U Citori line like the Lightning ..or what you might consider their typical field gun configurations ...and it was always built on the 20ga receiver ( and so were the 28ga and the .410 for the most part ).
Other than Nostalgia ...prior to having screw in chokes in shotguns / and when there wasn't much variety in commercial shells in 12ga or 20ga ( or at least not the variety of loads we have today in 12ga and 20ga ) like in the 1950's thru the 1960's ....the 16ga had a niche ( with a 1oz load ) in the field. Before screw in chokes - we all had "waterfowl guns", "Grouse guns", "Pheasant guns" , etc ...that were longer or shorter barrels, lighter or heavier guns, Full or Modified fixed chokes, etc....so the 16ga with a Mod choke in 1oz loads had its place. My first shotgun was a 16ga Bolt action with a Mod choke - when I was about 10 yrs old / and I still have it
These days with screw in chokes ...its easy to change a gun to a Mod, or a Full, or an open cyclinder....and in 20ga its easy to find 1 oz loads ....and its easy to find 1oz loads in a 12ga too....so the 16ga kind of gets squeezed out ....where you can do more with a 12ga today than you used to ...load it heavy or light like a 16ga or even a 20ga ....or a 20ga load it heavy or light like a 12ga or a 28ga.
The issue of the size of the receivers - is certainly an issue in field guns ...where guys want lighter guns to carry ...and a 12ga may be too heavy ...and sometimes a 16ga was made on a 12ga receiver or today, its often made on a 20ga receiver..../ so yes, there is some nostalgia for the old - lively swinging 16ga's ...but today, in my opinion, they get left out where a 12ga or a 20ga are just better buys ...and the ammo has come down in price for the 16ga ...but I doubt it'll ever be less expensive than 12ga or 20ga. But you still have options out there - to buy a new 16 ga ....BPS sells new in my area for around $600 and you can get a BPS in either 26" or 28" barrel ...2 3/4" chamber.
http://www.browning.com/products/cat...2&tid=211&bg=x