Erm, the new Mac Pro is much more expandable than the old one, they just moved to the external expandability as opposed to internal one. I have a legacy server running an old MP and a new one running the can and the new one is much more flexible.
well seems your definition of expandable is to plug in 10 devices and have a cable mess on your table.
my definition of expandable is to open my mac pro 2012 and have 1 ssd, 4 hard drives, 2 gpus. everything standard and upgradable to the state of the art for a good price.
i updated the xeons to the fastest possible model and upped my ram to 64gb.
my 2012 machine is probably way faster than yours now.
and hey, if i want cables for fun i can still plug in some stuff.