Just from reading their page and being familiar with the formats you mentioned:
vs. protobuf: ion is self describing, vs needing a schema
vs. thrift: similar, thrift needs a schema to interpret a binary file
both thrift and protobuf are really binary formats, though they have a canonical textual representation, it's not actually used to serialize. Sounds like ion supports serializing as text as a first class concept.
vs. msgpack: ion has a corresponding text format, whereas msgpack is only binary. Additionally, ion has a symbol type, msgpack doesn't.
I think the biggest benefit here is that it's a new chance for a format that fixes some of json's rough edges to gain critical mass. There's probably nothing ultra special about it that hasn't been solved in other formats, but maybe the timing will be right and everyone will just adopt it as a json replacement (sort of how people just gave up on xml and switch to json seemingly overnight). It's impossible to predict stuff like that.
Edit: upon noticing that it was released in 2016, it seems less likely everyone will jump on the ion bandwagon ...
If I'm not mistaken, there were plenty of text protobuf files internally used for a lot of things, and much much less anything less (okay, xml was prevalent for our team, maybe due to being java-inclined). Even seen examples of text protos pushed through the command line (it's possible, but need to get it right)
vs. protobuf: ion is self describing, vs needing a schema
vs. thrift: similar, thrift needs a schema to interpret a binary file
both thrift and protobuf are really binary formats, though they have a canonical textual representation, it's not actually used to serialize. Sounds like ion supports serializing as text as a first class concept.
vs. msgpack: ion has a corresponding text format, whereas msgpack is only binary. Additionally, ion has a symbol type, msgpack doesn't.
I think the biggest benefit here is that it's a new chance for a format that fixes some of json's rough edges to gain critical mass. There's probably nothing ultra special about it that hasn't been solved in other formats, but maybe the timing will be right and everyone will just adopt it as a json replacement (sort of how people just gave up on xml and switch to json seemingly overnight). It's impossible to predict stuff like that.
Edit: upon noticing that it was released in 2016, it seems less likely everyone will jump on the ion bandwagon ...