Earlier quoted context omitted.
From the perspective of the WebKit team, I think it would be about spending a lot of time and effort to support something that isn't part of their core mission, the standardised web. It would also saddle them with an extra maintenance & support burden for the foreseeable future, to the strategic benefit of nobody but Google. I think the original conversation was hampered by a miscommunication - it was never made clea…
Let me quote the relevant paragraph from their goals in full: Standards Compliance WebKit aims for compliance with relevant web standards, and support for new standards In addition to improving compliance, we participate in the web standards community to bring new technologies into standards, and to make sure new standards are practical to implement in our engine. We use regression testing to maintain our standards c…
Secondly I would agree that WebKit has its own OS X-related baggage, but that just goes to show that nobody's perfect. It's not an argument for adding more. I would also agree that in the hypothetical case of Dart support being added to WebKit that Google would be expected to maintain their code, just as Apple would be expected to maintain OS X stuff.
But again, I think the original conversation was had at cross-purposes. What started as a conversation about hosting a branch of WebKit to do some innovating turned into a conversation about standards and the broader web. In the former case it's a purely technical question of where the work is done, but in the latter, I think the "participate in the web standards community" bit comes in to play. Why did Google come directly to WebKit to ask about integrating Dart instead of talking to e.g. the W3C or WHATWG?