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...
It's not even the first debate. The ones not qualifying for the debates in the first place are in no position to get better to begin with. So I think the ones who do, and that includes Yang and Gabbard at this point, are better off as they can present their ideas. I think from the 19 who are named by the Wikipedia as important candidates + Biden (who is probably running), only 10 I think are safe by either unique donors or constantly polling high enough. As the polling criteria is very loose and it is still time to get donations, some more will qualify but five candidates will probably fail at this point and drop out. The ones that are in danger of not reaching the first debates are in my opinion Castro, Delaney, Gillibrand, Gravel, Hickenlooper, Inslee, Messam, Ryan, Swalwell and Williamson. Probably only half of them will make it to the debates.
The the next winnowing will be probably the criteria for the second round off debates.
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.
Fivethirtyeight has looked at past primaries and looked what early polling tells us. And adjusted for name recognition early polling gives a somewhat decent indication who might have a chance.
I'm interested in part 3 with conclusions and probably a polling average adjusted for name recognition for current candidates.