First of all, it's never been called open stock. It's just stock. And 20 years ago when I stared racing there was a class for beginners. It was called stock.
As you point out, every track is different. Some clubs only had stock, while the club I stared with had stock, modified, and pro.
A cost effective class is something for tracks and clubs to try. It may not work everywhere, but it may be just the thing for some.
And why is there this huge resistance to run 19 turn? I can see why you wouldn't want to run mod (too hard on equipment) but 19 turn is not that much faster than stock.
At my local track (South Shore Hobby) after years of trying we finally got all the good TC drivers to run 19 turn. For a while there was only a 19 turn class. But then a handful of new kids came in and got involved with racing. 19 turn was too fast for them, so they asked if they could run stock. By the end of last season there were 2 distinct classes in TC, 19 turn for the experienced racers, and now a new stock class for the newcomers. In all ther are now 8 new racers!
Yea it's fine for 20 guys to get together and have fun racing cars, but unless you do something different it will always be the same 20 guys. You won't see any growth.