if it was Casual then it wouldn't be there in the first place, IV checking is needed Imo, given many players who do it, are the ones that are not the casual players but the serious ones who spend.
This isn't Pokemon Showdown/competitive cart play, bro. Go is very simplified compared to the main series games, and a good majority of players either haven't touched a Pokemon game at all, or haven't played since the 90s. Kinda doubt an IV checker is the first priority to Niantic, especially considering the slew of bugs that still need to be addressed.
If anything, someone online is bound to create an IV checker for Go (if it hasn't been done already) at some point. I doubt we'll see a checker in-game; having perfect IV worries on top of the randomized moves would likely drive away some of the more casual players (aka, a significant portion of the game's fanbase).