As long as the tomato is sufficiently ripe you can save seeds.
This tomato is COMPLETELY ripe and will not get any pinker. Flavor/texture will not improve and will in fact deteriorate if I waited. How'd it taste? Absolutely magnificent. I think the neighbors heard me giggling with excitement and probably wonder if I've lost it. Didn't know a tomato could taste this good.
Not to upstage that Brandywine pink, but Cherokee Purple also has green shoulders when fully ripe. You would not want to wait any longer than this to eat it:
It tasted as mind-blowingly good as it looks. Complete, even ripening is a gene that many heirloom tomato varieties do NOT possess.