I'd call it the "make a name before shit gets serious" game. And position yourself and your policies.
Some will probably drop out soon. Delaney, Gillibrand, Williamson, Inslee and Hickenlooper are constantly polling very badly without any improvements. I don't think they will last very long anymore. They might wait for the first debate and see the reactions, but if they don't improve from there I'm sure they'll see the writing on the wall, too.
I don't know what to make out of Messam and Ryan yet, they're not even named in most polls yet. And now with Swalwell, there's probably yet another for the "other" list, at least for now...
From the candidates perspective, it's even pre-game for the "make a name for yourself" period. This is really the tail end of the exploratory committee period. We always have front runners at this point that never make it to the finals and nobodies who go the distance. Starting in the summer, that's when we move into the real "make a name for yourself" period. That's when it starts to count. When ads start rolling. Interviews happen. When the first debates start to shape the field.
And I agree that those you listed (plus Castro) will probably drop this summer.
Massimus - "Trump already has democrat support."