I think there are limits, though, to caring about people's preferences. To me, dealing with people who make me jump through hoops to successfully communicate with them is an incredibly draining, patience-testing, tedious activity. For some people it's worth it, and for others it's not; I've definitely reduced my level of interaction with some people due to this.
I used to be very introverted and shy, and I still hate doing things like answering the phone or talking in person to people I don't know (and I still work on improving there). But I've learned that communicating with the people around me who care about me (and vice versa) is nothing to be anxious about. It's taken literally decades for me to get here (I now consider myself a somewhat-shy extrovert), but I do feel that my life is better having (mostly) left that anxiety behind. I don't see this as some "personal preference" type of thing; I mean, social anxiety disorder is, well, actually a disorder listed in the DSM.
Your analogy about Candy Crush doesn't really speak to me, because I absolutely agree that there's nothing wrong with killing time with a silly game when you're in a situation where you have to wait (with the exception of games that deliberately and maliciously hook into addictive tendencies). But I do think that an inability/aversion/anxiety around basic communication between friends is actually a problem. I'm not saying that people who have these issues are bad people or anything like that, but I would hope that people with those issues actually view them as issues, and not just a "style of communication" or whatever.
Beyond that, one possibility is that this app just won't gain much traction, and it'll either fail or find a small niche. Otherwise, I just don't see this as something that people will use in moderation. I feel like the people who do genuinely need it (due to introversion or social anxiety or something like that) will use it frequently, and will end up bailing on more activities than they would have otherwise (which sometimes will be good and sometimes will be bad). And I think other people, who don't really have introversion issues, will use it as a way to make rude flakiness easier to justify, and have a normalizing effect on that kind of behavior.