The blog post gives an example of how the current approach makes dependencies incompatible.

> if someone publishes an alternative to serde (say, nextserde) then all crates which have added support for serde also need to add support for nextserde. Adding support for every new serialization library in existence is unrealistic

If I use serde, I cannot use a crate that only implements nextserde.

If I want to use nextserde, I lose the ability to use all the crates that only implement serde.