There are so many unique urls that finding another user who have commented on that specific one will be more or less impossible.
I am not handling all unique URLs as truly unique - they are normalised. So actual pages where you would want to leave comments - say some business' home page or a Twitter user's feed - will have a unique URL and will allow multiple users to discuss content. Something like https://youtu.be/PcdMU-H9Jts and https://youtu.be/PcdMU-H9Jts?t=899 are kept as aliases in my DB and will have the same comment tree.
But as far as I know, it hasn't worked for the others. And as far as I know, they are not only similar things - but identical. What distinguishes your implementation? What actually is the advantage of this approach?
I haven't seen the iOS integration before, but honestly - I would never use that, what is the chance of finding comments? 0.0000001%?
I always wanted something like this to become popular and gain a user-base because it might lead to a more community-feeling web.
Here's hoping you accomplished it. Cheers.