The soldered on SSD is a dealbreaker. Plain and simple. There goes another option to replace my old MBP...
I think it is better to have a soldered SSD than soldered RAM. You can always expand storage via an external drive, but you can't get more RAM.
Of course it would be great to being able to replace BOTH, but if I had to chose I'd pick RAM over SSD.
By the way, I think since they're using the T2 even for the disk we can't expect to be able to replace the storage in the future.