hi, i'm the founder of this site and am actually quite curious what you mean by this. do you think the feminine design will scare men away? or do you think the name will scare women away?
Further, if you start with a domain like inlu.st, you are eliminating the % of women that actually care about long term relationships over one night stands. That is a very large %.
Just my opinion. I have no data for you.
I think that both the and community requirements can be very different for casual contact and ltrs, but there will be some natural mobility between those.
However I wouldn't necessarily trust my intuition and would prefer testing it.