There is no break from previews. Previews are life, life is previews.
3 CMC strikes me as a very relevant threshold in terms of upping the playability of a planeswalker in vintage. Flashing back two cantrips seems pretty good, middle ability could potentially sting an opposing walker at least, and first ability obviously helps out with the ever-growing roster of powerful walkers out there. Seems good?
Also worth mentioning: this is one of three Chandra planeswalkers previewed today from Core 2020. I didn't find the other two very interesting (for Vintage or just in general), but that probably implies at least fifteen planeswalkers in the next set.