Looking at the walkthrough, the harem will be fine. In the next update i wonder will Rachel confront Dear Brother right away the next day or give him the cold shoulder with him finding out for himself. Eventually the girls would had to start finding out about each other one way or another even with the soundproof walls. Also, not just 4 main girls (Mom/Smith, Rachel, Bella, Liza), there's the others like Rachel's friends (Ana, Alina, now Kira), Adriana (with the Holmes identity plot with Mom), Riley (ex-coworker), Iris (won't be a big lost). Have that sorted out & all go back to Belugio with Nia & Rebeca waiting.
Will Megan only be available in Bella's hardcore route or will something happen later in the romance route? I guess Hazel (Bella's blackmailer's mom) was a one-time thing, but wasn't there a sextape somewhere? I wonder will the girls (Sasha, Miley, Sabine) from our Protagonist's past make an appearance in present time.
There's also still the plot with the batty old teacher & country's moral policing & anti-porn law going on, Protagonist revealing he's Mr Holmes to Mom & Adrianna, and the developing romances with Mom & Liza.
As far as looks goes for me it's Nia, Kira, Riley, Rachel, Adriana, Rebeca, Sasha, Bella, Mom/Smith, Liza, Alina, Ana.
Also, i like that in Sisterly Lust you can play every girls route in a single playthrough without the need to save scum (minus Bella's hardcore route). I wish more visual novels would follow that same format, instead of lots of branching plots that'd require a walkthrough.