Different cultures have distinct visual aesthetics that mass-market filter apps don't capture. Build an app offering filters modeled after specific regional art styles and photographic traditions.
Start with Korean beauty filters as proven by the source app's success, then expand to other markets.
Monetize through premium filter packs and in-app purchases.
MVP could be a simple iOS app with 3-5 culturally-distinct filter options.
Biggest risk is competing with free alternatives, so emphasize authentic cultural representation.