> Frankly I should think that many Muslims would find this entire notion offensive.
Many people find anything offensive, but I don't see any particularly good reason to think there is anything particularly deserving of it in this concept.
> Just because someone is Muslim doesn't mean they (a) necessarily want to find a muslim partner
I would think that even Muslims who do not want exclusively to find a Muslim partner would recognize that there are Muslims who do wish that.
> IMHO in many traditional societies young people want to shake off the controlling habits of former generations and such an app would actually be a concrete step backwards.
Allowing people who don't share their open attitude toward dating he opportunity to have a dating forum that supports their preferences does not prevent those with open attitudes from pursuing more open venues, which are not in short supply.
Christian Mingle doesn't stop Christians that whose dating interested isn't religiously restrictive from using any of the vast area of open-preference dating apps in the universe, the Muslim equivalent would be no different in that regard.