My ideal "harem" would be a game where all of the girls are like Odette, and actively attempt to set you up with each other. Unfortunately that's something you need to set up in the initial design phase of the story and it's far too late to steer SU into that direction.
Yes, Odette's active support would make a
harmonic harem a bit more possible. I expect that Odette would need to be a main LI and introduced earlier. Roxxy can't fulfil that role. She's too caught up with her own status/standing and seems to share him with her friends to reinforce her status as their leader and benefactor rather than out of a desire to make them happy. Also, as you suggest, you'd need more than one "Odette" to maintain the process.
In My New Family, Killer7 seems to come close, he has a number of key members participating in a loving chain reaction--largely about the women wanting to share the healing, the positive feelings they get with the MC. Unfortunately, too many of the relationships in StS are discrete, largely unconnected to any other LIs. We have a few connected relationships [(Odette & Grace) (Roxxy, Becca, & Missy) (Debbie & Diane)], but too few to reach a sustainable "critical mass."
I can see reasons why so many expect Eve to be the facilitator. She's the most unconventional of the students and since Odette does a lot to project her own perspective onto her, we want to take Odette's word for Eve's blossoming nature. It's also logical to want to unite the 2/3-1/3 configuration in the house to 3/3. The same with the home 2/3-1/3 situation.
The fact that we have to chose
one date for the "prom"/"sorority dance" telegraphs that we're not likely to get that beach house orgy/reverse gangbang.