Modern Horizons will be a new set that bypasses standard, but will be tournament legal in all eternal formats starting with Modern. Expectations are for new archetypes to form in Modern from the set, with hopes for new archetypes in all eternal formats.
Obviously, this set is a great direction for Wizards to continue to develop the eternal formats and a much better way of doing it than Commander and strangely designed conspiracy/battle bond expansions.
Release is June 14, 2019.
Only 2 card have been spoiled/leaked so far. Let's not focus on the awesome implication of sets designed to create new archetypes in Eternal formats and focus solely on this new card: Cabal Therapist will look strikingly familiar to most vintage players.
Obvious first implications are that dredge gets MORE cabal therapy effects. But it cannot be cast from the graveyard. Would this enable a deck like Nic Fit in Legacy to have enough cards to become a playable deck in Vintage (Nic Fit abuses Veteran Explorer)?
The obvious difference between the two is cabal therapy gets cast from the graveyard, and can immediatly be cast again with flashback. Whereas Therapist can be used every turn, but provides no immediate information.