I guess I'm not like most people ..... I keep things til they fall apart .... and can't be put back together because they are too rusted .... oh, and I do a lot of rustproofing with fluid film.
If you've got a perfectly good DIY battery, I don't understand not wanting to get as much life out of it as possible.
If I'm still alive to be using mine, I plan on using it beyond the point where it has 80% capacity.
I suspect that as these batteries get more and more popular they will get more expensive. I could be wrong, but it seems to me they are a low price point that will be going up.
If they come up with something that is 10 x more energy dense and is also cheaper ..... I won't replace mine til the bus bars fall off.