That's a fair point, and I hadn't though that all the way through - having an eGPU now fully supported mitigates the need for a heavy-duty built in. It does add another cost though (but at least you can upgrade the two separately. Wonder if it 'just works' and how easy it is to use (i.e. can you unplug without shutting down)?
I've seen some videos of it being hot swapped (like they just unplug the eGPU). But I'm a bit skeptical that this is quite going to reach "just works" this year. Seems still something for the pros to use in their heavy duty work flow.
Another interesting this is that the 13" MacBook Pro is going to have vastly more powerful GPU than the 15" MacBook Pro if you use an eGPU, yet the cost of 13 + eGPU will be about the same. If your Macbook Pro spends most of its life as really a desktop, you could get an eGPU and stick that under your desk or somewhere out of sight.