Was The Final Fantasy 7 Rebirth Trailer THAT Good? 

I have a feeling he was talking about Aerith. Given some stuff that happened in Remake and Intergrade. I feel this is a sequel to FFVII. But it is being presented in the same way that Evangelion did it’s Rebuild movies. I could be wrong. But this seems to be an alternate reality where both Sephiroth and Aerith are the constants. Time will tell.

as long as we realize the timeline is just flying all over the place, it'll work. the gameplay will be good for those that liked 7

Sephiroth is talking about Tifa. Both in the JP version and the FR version he says "Tifa" he doesn't use a pronoun. So this is 100% Tifa. Also, he'stalking about the Nibelheim incident, where he hit tifa (like in the trailer) with masamune, she was presumed dead, Neither Cloud or even Sephiroth saw her get back on her feet as Sephiroth got thrown in the river of life by Cloud and cloud got Knocked out by Sepiroth. Sephiroth is trying o f*ck with clouds memories like "You saw me slice her, you saw her dea, you never saw her getting heal, so how can she be right there besides you". This is not the first nor the last time Sephiroth tries the f*ck with Cloud's memories/emotion.