Originally Posted by carracer
My concern is over the years the block threads will wear out and then what
Well, put Brass plugs in the holes. The likelihood of Brass wearing out the cast iron of the engine block is about nil. After 100 years of removing/replacing the brass plugs, they'll wear out and you can replace just the plugs.
I'm not a fan of these kinds of drain valves. When I pull my drain plugs, I normally have to stick a screwdriver in the hole to knock the scale loose before the engine will drain correctly. With a valve in place, you'd never be able to do that.