It would really encourage people not looking for marriage to use the app for dating, since their use would be free. It would, of course, also result in the site taking steps to eliminate them, maybe even tolerating false positives. In the end would it produce good results? Dunno.

(Also would add legal complications most dating sites, regardless of model, don't deal with because of the Statute of Frauds in relation to contracts in consideration of marriage.)

Some of the modern Indian dating apps seem to follow this approach and do quite well. It’s likely more accepted there because of the tradition of arranged marriages. Western audiences might find it strange.