"Wait why portable?"
To simplify the blockchain hosting (Nodes) thing and increase participation.
Combined Data Storage Device, Internet device & Solar power = Portable.
Ahh but solar power isn't exactly strong enough to power a device. Even if you somehow discover a new material to do it, you'll be holding it and have it facing the sun for hours a day. Solar power isn't readily available either. The cost of internet would just make this whole thing unfeasible.
Even if its not portable, I'm sure the participation would still be relatively good. Bitnodes (not sure who they are now) used to have such a device but its basically just a raspberry pi.
"The largest 3.5' HDD is 10TB, go figure."
Notice my use of the word "Imagine." However, a company could combine several of HDD to increase the capacity to let say 100TB.
Okay, its quite out of proportion to say 100TB right now since the blockchain is still relatively smaller than even 10TB. Lets just put it at 10TB.
The current 10TB HDD could cost upwards of $200 and I really really don't recommend anyone carrying it around. Its not meant to be portable. Even if its an SSD, 10TB is quite far of right now, 4TB being a thousand dollars.