The app that comes closest to a luxury service that I can think of is Superhuman, which charges its users $30 a month for an email client (which you could also get for free by just using Gmail). But there’s a difference to other software products: Superhuman has signal distribution built in. Every time you send an email via Superhuman, your recipient will notice a little “Sent via Superhuman” in your signature.
Superhuman is the closest thing Julian can think of to a luxury software product. One reason might be that Superhuman has some signalling built in: It will add a little "sent by superhuman" to your signature.