I saw baby bettas when I was out recently and part of me was horrified (so many are going to go to awful homes!), and another part really loved the idea of watching a baby grow up. So pretty much the usual reaction whenever I see live animals for sale.
A divided 5g would be enough space for two bettas I believe, but my concern is what if the baby turns out to be female- I already have an adult male, and no room for more tanks. Obviously they wouldn't be able to get to each other but would sharing the same water stress them out? I could always find an adult boy if that's the case, but watching a baby grow would be quite the experience.