[quote=@BrokenPromise]
Power scales tend to be a problem regardless of what you do.
[/quote]
It has always been a trend of the genre to make the "Next best thing, totally guys, my character is awesome!" type scenario, [@DocRock]. I am not so confident that implementing statistics and mechanics of any kind will do much to resolve the issue of having such disparate powers and dynamics in play. It comes down to, in all honesty, having reasonable players and not ones who are attempting to "power game" roleplaying topics, which is far easier said than done. More often than not, these kinds of players tend to be younger, more inexperienced, and prone to abuse of well tread tropes and cliches that others now cringe at. 

Continued, the community you are speaking to and about here on the Roleplayer Guild tends to have a great number of factors in play that work against the proposal of something more mechanical in nature, among the others noted earlier. People tend to not like anything too complicated in that matter and a fair number are a bit difficult to convince to not create wildly disparate levels of power, let alone use them respectfully; there is no real consequence for them exploiting multiverse and power based issues other than being shuffled out of a topic. They can and do simply go elsewhere on the forum, meanwhile the prior topic tends to suffer due to the frustrations involved and the fact it readily upset the plot.

I suspect, in no small or better way to put it, to select and cater to a number of people you can trust for such a roleplay. Failing that, it is mostly left to you to construct something and govern it with the hopes of reaching those desired results. It appears to me that this would not be terribly difficult for you between your experience and motivation, to say nothing of the fact that it is what you appeal to, so how you go about it is the larger element I would suggest looking into. The short of this being is vet your players wisely, reach out and appeal to those you would like to play with, be active and proactive, and develop an identity for the topic.