I don't have a strong opinion on whether you should build it or not (I have a Mac but won't use it, which has almost nothing to do with whether it's a good idea or not), but here's some other admittedly unsolicited advice (and of course I recognize that you may know all of this already):
Remember that most people who think it's a bad idea won't respond, and people who do respond are doing so because they're interested, or think they are. So there's some bias to account for. And secondly people who say they want something can't really be trusted; it costs nothing to upvote you and people are really quick to say "yes, I'd buy/use that" and though they certainly mean it at the time, it's very often turns out to be untrue when it's actually time to download and install it.
Of course, it might work anyway; I'm just saying that I doubt that asking HN whether you should code it is a good predictor.