It sucks that the SSD is (presumably) not upgradeable anymore. Apple generally charges a ton for the larger SSD offerings, but it used to be that you could just buy a base model and replace the thing later.
No thanks, not for my boot drive.
This is the same concept as L1 -> L2 -> L3 Cache -> RAM -> Disk.
When you need something, bump it up, when you don't, move it away.
Do you need a 512GB boot drive?
I have a base level 2 port MBP from work and having to do any work with large files has been a nightmare because of this, having to juggle power/monitor and storage constantly.