Remembrance was originally intended to be paid DLC for Obsession, not a free content patch. So no, no one will get Remembrance for free (except Patreon supporters who paid the game cost in membership fees prior to the release announcement).
Remembrance was changed from paid DLC to a full sequel because the scope of both games grew far beyond my original intentions. I initially thought Obsession would be half the length that it is and Remembrance would be like 25% of that length.
Now I expect Remembrance to be even longer than Obsession. Remembrance will likely (subject to change as always) include both a full route for Alexander and Victor on release. 6 routes instead of 4 with a significantly larger number of CGs, plus the voice acting and the other listed improvements on the store page.
I am including a (very short) abridged version of Obsession within Remembrance for any players who couldn’t stomach the extreme content of Obsession. So playing Obsession is optional. (This abridged version contains no variation endings, side content, etc. It’s a single short linear summary of the world and Ethereal situation.)