Adding to what Xophmeister said, IPA isn't just a notation, it's also a tool of thought. First, to efficiently quantize the stream of sound you need mental "buckets" to put the sounds to, and IPA provides your those buckets. Second, it may seem as if we hear "objectively", but in fact what you hear is very much affected by your language upbringing; for example, a ton of Americans can't really differentiate "pin" and "pen" even if the words are pronounced as in Standard American — they don't have a concept of the sound needed. IPA gives you those concepts.

> Can't help but feel that IPA will go the way of cursive once tools like this propagate.

IPA is necessary in phonetic and phonological research. You need a way to transcribe and abstract sounds consistently; you can't just submit a recording, along with your paper, to a journal.

There are still languages with no writing system of their own out there (or with a borrowed script that does not necessarily fit their sounds very well). IPA is not perfect but quite relevant for research and language documentation.