I keep seeing the argument that more good than bad will come out of having mixed seating in chasunahs because it it an “controlled environment”. I don’t think that this makes a difference, seeing as once a boy and girl have each others name and phone number, they are free to continue their relationship anywhere and anyway they chose.
I also have seen mixed chasunahs compared to kosher “singles events”. However, I think the key factor that makes these events kosher is that all the singles there are seriously interested in getting married, while the singles at a chasunah can be there for any reason (and the mixed seating would just be another reason for not so serious singles to come).