Pokemon-EX aren't going anywhere, as future products slated for fall release have been referring to things like M Mawile-EX, M Aerodactyl-EX, and Palkia-EX, plus Hoopa-EX from the current Ancient Origins set has an ability specifically meant to synergize with Pokemon-EX. BREAK Pokemon, as mentioned by others, are just an additional mechanic.
However, one question I have about this mechanic that I haven't seen answered yet: back in the days of Lv.X, it was ruled that, for example, Gardevoir and Gardevoir Lv.X were the same Pokemon, and therefore you were limited to a total of 4 Gardevoir and Gardevoir Lv.X in your deck. Are Zoroark and Zoroark BREAK going to be considered the same Pokemon, as Lv.X were, or will you be able to have 4 of each in your deck?