Based on what?I think that this trailer will reveal more than just Sirfetch'd.
Every trailer in the last couple of months has revealed minimal details at best. 1-2 Pokémon at a time.
If I had a dollar for every time some naive person on here posted “I think this next trailer will show us the middle stage of the starters / the regional bug / the regional rodent / the box legendary typings” I would have at least $100 by now. I’m still waiting to see any of those things revealed.
Expect very, very little from this upcoming trailer. Worst case scenario you’ll be correct, best case scenario you’ll be wrong and pleasantly surprised.