Hardware-dependent block difficulty?
No, difficulty is a network-wide consensus rule. POW mining helps solve the issue of sybil attacks, whereas your idea opens up mining to sybil attacks:

Your idea would create a level playing field for all devices (regardless of computing power), so if I want to expand my mining operation, I would just want to run thousands of mining nodes. Hardware doesn't matter, so I could just use cheap computers, or better yet, a botnet. The more nodes I can make, the better! 

Additionally, how can you be sure nodes aren't lying about the hashrate available to them? How can you be sure a user hasn't rewritten the source code of their client to artificially lower the difficulty? Etc.