How is dual proprietary/GPL anything other than strictly less obnoxious than proprietary alone? You can, after all, stick your fingers in your ears and pretend that it's proprietary alone, and there will be no observable difference.
I think the obnoxious part is not being entirely upfront and clear about what you're looking to do. Sencha make no secret of the fact they're a business, with Meteor you need to infer it from a vaguely worded FAQ point and the licence type.