This seems like right UX to me - a separate subscription management area. From the article it sounds like you don't have to select UTXOs or create a UTXO for the exact amount because the adaptor signature can limit the spend from a UTXO.

I think I'd prefer to just see it all as one balance because I can still spend all the funds even if I've sent Netflix the adaptor signature. The wallet would just have to warn me when a spend will prevent me from paying for a subscription.