I feel like a lot of people are missing the point.
Power creep by itself is not what this proposal is about (although it does tie in somewhat, but not being discussed atm).
The proposal aims to establish a "stable system", a base from which all future balancing will be done. For that to be a possibility the game has to work in completely the same manner in all tiers of gear, no matter the absolute power level.
In simple terms, if a guy in Anni can dish out 300 DPS (or HPS or any other combat performance metric) to another guy in Anni and the abilities and scaling secondary stats (crit, parry, crit damage) are balanced according to that - which is what the community and the devs are doing in the balance forums - then this balance will be broken if a guy in Sov can dish out a 1000 DPS to another guy in Sov. Which means that all the balancing being done right now is pointless since it would have to be redone for every new tier of gear. This is what Azarael means when he says that the fate of the balance forums hinges on solving this issue.
The alternative is to close down the balance forums and wait till Sov comes out to balance the game. Trust in the devs to be able to
somewhat internally balance everything until then and trust in their vision of the game.
Now sure, power-creep would be easier to address if this system was to be established and the relative power between tiers of gear could be capped to prevent the system from breaking too much even between different power levels (this idea particularly appeals to me) but that's not the focus of the proposal.
As for the concerns about a "hidden" systems that have been expressed, I believe there's a lot of seemingly hidden systems in the game already. How many people would be able to explain how toughness works? Strikethrough? Offensive stat ability coefficents? There's information out there and some people are aware of it or are trying to learn about it. Others simply shoot greenskins and don't ask intricate questions about the projectile velocity and force of impact.
Besides, such a system could be tied into the ToK/paperdoll functionality with some added tooltip calculations once client control is reached. For example the current wording on the armor tooltip is:
"Reduces Physical damage dealt to you by enemies.
Physical Damage Reduced: 40%"
Physical Damage Reduced against an equally geared player: 25%
I imagine adding something similar to tooltips wouldn't be too difficult.
I don't see hidden systems being an issue at all, not with client control. Hell you could have a page in ToK explaining all of this by tying it into the Ward system Mythic implemented.