If this guys is going off about how it shaves a week or so off a 5 week project, problems that appear on bigger apps might not be high on his priority list.
I wonder if Meteor will end up introducing security holes like ASP.NET, as developers forget there's an abstraction and clients can't be trusted? (In ASP.NET, things like being able to screw with viewstate or fire events for disabled controls.)
I still have the hope for a unified platform. But I'd much prefer it to be on a solid language that compiles down to JS. I'm not sure it's an unattainable goal. I think you nailed it with "seamless" and "invisible" - abstracting major things like client versus server, or local versus network, can really end up biting developers.