We've already been pursuing the jni-sys 0.4 upgrade in #433 but won't commit to it until the matching jni 0.22 drops to match. As you can tell from the download graph at https://crates.io/crates/jni-sys no-one uses 0.4.0 yet 0.3.0 still sees upwards of 80k downloads every working day.

Without justification I see no need to bump thiserror - which would be very hard to get done at once across the entire ecosystem - and will instead spend some time investigating whether we can support both using version ranges.