Go ahead. It'll be a long time until I get to dart. Matching versions is nice, but I suspect the bindings will drift, so if that doesn't happen just document what version it's on. I suspect that for anything but Python we're going to find out that bindings need incompatible changes apart from Synthizer itself. Python won't because Python gets special status for weird reasons.
That said, two things. First, Synthizer 0.9 is going to break the API. No way around it. I don't know the timeline, but call it sometime in the next 6 weeks tops. Second, I would appreciate it if you didn't upload to package managers unless you're sure you're going to be around to maintain it. I'd rather not end up with a bunch of official-looking packages that are n versions out of date. That applies to everyone, not just you. It doesn't exactly do harm, but it is still kind of meh when you find something that looks like it does what you want but it hasn't been updated in a year and is missing all the features. Don't get me wrong, not asking for signatures in blood, but do think about whether uploading now is going to provide a good developer experience and so on.