No He Means Like Kanto Had The 3 Ledgendary Birds, Johto Had The 3 Ledgendary Dogs, And Hoenn Had The 3 Ledgendary Elemental Regi's....
Heres A Little Chart Of What Old Ledgendary Is The New One....
(E.G....Mewtwo Is The New Lucario)
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Mew,Celebi,Jirachi= Manaphy
Mewtwo,Deoxys= Lucario
Zapdos,Articuno,Moltres,Suicune,Raikou,Entei= Unknown (Thats What Threads Asking)
Ho-Oh, Lugia, Kyrogre, Groudon= Parukia And Diaruga
Latios, Latias= Unknown (doubt They Will Make Ones Like These)
Rayquazza= Unknown (Highly Possible Making One Like This As The Game Seems To Have Many Dragons)
Hope That Helps...And Im Guessing The 3 Trio Ledgendarys Will Be Either Dragons Or Something To Do With Space...