I've been obsessed with this feeling that splintered shards will be "reformed" at some point. I was always totally unsure which, Honor being the most obvious, but I'm thinking that Ambition may as well. The Night Brigade is searching for a specific Dawnshard to combat The Evil of Threnody, right. The very same one that disallowed Hoid to ever kill or even eat meat. What if that one and the one Rysn has (change) are somehow combined and the result isn't just the eradication of The Evil, but it actually pulls the splintered pieces of Ambition back together in a new vessel. The results could be that Ambition would go after Odium (who wins in book 5, lets be real) and Mercy for the whole, you know, killing it once way back when. Just sayin, BS has something up his sleeve in terms of Threnody.
... also, I think that Autonomy is somehow tapping Ambitions unused investiture (which is most likely like a gas cloud in space) which is why she's able to spread herself so far. If Ambition is reformed, I don't feel that they'd have a huge problem with that (I mean, it's ambitious of Autonomy to do so) but Autonomy would be kinda stormed.