Could this card be constructed playable? Hard to say.
Well, there’s plenty of cards that work well with it.
… and plenty of others.
It helps there are some of the best cards in standard in that list. It doesn’t help that the rest are either hard to use or pretty much useless on their own, so its actually hard to say what is the right way to do this deck. Except, if you are going casual, in which case just do a 5C Butts and kill yourself with all the five color pain lands. (Also, if you go that route, try out Mardu Ascendancy.)
Doesn’t mean I can’t brew.
Four Assault Formations isn’t enough to make a winning deck. I’d be happier with eight wincons. We can’t really do that, so we have to survive the early turns until we find one (or can tutor for one). Gladly, that should be pretty easy as we have plenty of big early creatures. Also, we have some ramp, so that we can hopefully get to six mana for the tutor, if needed. Otherwise the curve is very low and the deck actually probably needs some tuning. Perhaps take out some of the lands and put Whisperer of the Wilds in their stead.
The mana here is very awkward as you’d like B for turn one for the Ancestor, and then either double R or double G on turn three for either Courser or Flamespeaker. This is especially awkward since there aren’t that many red cards that would be good in this deck, so were really pushing the manabase for basically two cards. That’s probably not what you want to do in general, but I’d like to try this out.
The Sidisi’s Pet is there to mitigate some of the pain from the Mana Confluence. The manabase might be very bad, but I’d need time to figure it out. Shards aren’t the easiest thing to do in this current format. This would probably be better if you just dropped the red or only used the Break Through the Line.
You good always do a Sultai or Simic versions as well. They would probably work well, because you can use the scry to dig to your wincons, but I’m guessing two lists is enough for now.
Besides not finding your wincon, the obvious problem with this style of deck is that most of the cards are pretty useless in this kind of environment. You can’t really win with a bunch of 0-power creatures…