...
21's plan, as stated, is pure bullshit. The only question is whether they know it or not.
Let's do an order-of-magnitude calculation
An
article from Life Hacker reports that it costs about $0.50 to keep your phone charged-up for a year:

...
~= $107,000,000 per year
This means that the expected revenue is
not insignificant.
...and this analysis is only considering phones rather than all the other devices that could also be set up with this.
The > 43% of hashpower centralized in a single entity might concern folks.