Well, I just finished the Memory Sequence called Bianca's Man, which I think is MS #10. The trophy listing would have me believe that there are at least 4, possibly 5 more Memory Sequences to go.
Yet, that hasn't stopped me from basically wrapping up the collection aspect of the game.
The villa's at 99% (only things missing are the remaining assassination portraits up in the attic). I have all 330/330 chests (though there are actually quite a few more than that in the game), all 100 feathers, all 66/66 viewpoints, all 20 glyphs solved, all 30 codex pages decrypted (and the corresponding puzzle solved), both models, all 6 seals, and every single weapon, armor, piece of equipment, and to my knowledge, pouch/container upgrade. All villa renovations as well, of course.
I did every single skill based-trophy as well, and all that remain are 4. 3 of them seem to pertain to story sequences, and the last is the Platinum trophy, of course.
Strange that I've got so much done, yet seemingly so much game left to go! I'm guessing that with the exploration aspect basically behind me, the remaining Memory Sequences will all be short, sweet, and mostly story-driven.