It is probably possible to tie to the amount of coins per each address. Limit available search space to the amount of coins per address. Till the next block.
Block find rewards are held back for x amount of found blocks by that user. Last x blocks never get funded to you and end up burnt; unless in the future you start back up again. This should [at first thought] all but obliterate the abuse of generating a new address for the purpose of mining; because too fast; no pay; not enough blocks per address? no pay.... something along those lines anyways. I am just trying to keep it simple until the nuances start to take hold and things get serious... but the endgame is everyone has an equal chance. You could calc a result with a slower device; because it's salt can do wonders for odds.
MAybe build in a POS-type mechanism: If you keep those fresh earned coins in your same account for longer; the reward goes up a touch after 'y' blocks... also helps keep the people in check trying to mine too much too fast.
This is a small thought that may help with it. So far; there's no logical way to approach a "limited devices per user" thing; we will always have one or another person(s) with more hardware and more funding.
Maybe we should get a thread together separate than this; But in my eyes; fighting the selfish nature of "underground mining hardware/software", I think falls very in line with how things have been going through the year and its why I have been discussing it here.
It's a tough cookie to wrap your head around penalizing for calculating speed. This is why I think it should be based of a standard but very precise timebase. Things like microcontrollers and whatnot's internal clocks; often suffer from voltage drift and a slew of other things. I can't stress the emphasis of a good clock.
I do agree that times have definitely been slow in the altcoin world; mainly because of the overall market being where it has been, and the countless amounts of altcoins that keep getting introduced; as well as the fact that asics/FPGA's have always shown that they basically end up taking over the greater share of earnings and making the gpu's less profitable..... but to everyone; remember; didn't this happen before? How did we recuperate then? How do you think it will play out this time? I smell a similar ride. The idea is to keep in touch with what actually becomes something; and what is just there to try and pyramid yourself over someone else and sell off.
Legitimately in my honest opinion; 95% of altcoins, are worthless and only carry a value because people still buy them. Most of those; started as a copy-and-paste pipe-dream with no actual ever widespread use of them but to simply use on an exchange to trade for another. Most I see that have some type of advertised use, or whatever else; legitimately [in my eyes] are farts in the wind, only they are less useful than a fart in the wind.
Sorry for the rambling =P