No clue how to tell which apps are 32bit vs 64bit, but yes I think this is why Apple has been very proactive in the past few months telling us that some apps have not been updated in a very long time and might not work correctly. The way I look at it, many, perhaps most, of those apps will be abandon-ware or apps written in a garage or basement and not well maintained. The professionally designed apps, the ones I use the most, should be better maintained and ready for iOS 11. Fortunately, for those of us who will not beta test, we still have until early Autumn before iOS 11 is released. I tend to wait a few weeks afterwards to give them time to exorcise the gremlins first! That should be plenty of time for the developers to get their old and not well maintained apps updated. If they don't, then I really don't think I would want to run their abandon-ware any more. I really cannot think of any old apps like that I want to keep. They were so poorly maintained, or out right abandoned, so I have long since stopped using them opting for better and more up to date alternatives.