This interquel is clearly NOT 5th edition. They say they are considering the fifth for a future BG3 or another game.So you are saying people will be playing 2nd edition in BG1 then 5e in BG:Tape then 2e again in BG2 ?
If they are not totally insane they will make the interquel 2nd edition (and not, say, 3.5) like the others, in order to at least try to give a sense of continuity.