OK I'll take a shot at this. As I think most overpowered/broken optimization exercises stem from unexpected rules mixes, all interactions between different rules sections are removed. Say through these three things:
1) All powers a character has are determined by their class/path/destiny, race and theme. Basic attacks no longer exist and charge is not a combat option. Even opportunity attacks are gone. Instead each character which thematically needs one of the lost attack options can take an appropriately designed power tied to their aforementioned class, race or theme. For any "why can't I do this" situation, the DM is encouraged to use the improvised action section in the DMG.
2) feats are gone. Instead characters get specialisation points regularly - let's say the same progression as feats are now. (Yes I'm just changing names to keep the ideas separate.) Each power has at least one specialisation option which is enabled by allocating a specialisation point to it. As other game rules are forbidden to interact with the specifics of a power, designers can more accurately determine balance for powers and their specialisations. Also characters can choose to truly specialise in their favorite tactic, diversify and spread their improvements, create consistently strong at-will or truly impressive daily's - etc.
3) Magic items add options in the form of new powers only. They have no effect on the attack or damage modifiers of powers other than their own, so the enhancement and item bonuses are gone, necessitating the 'Re-do the combat math' as well.
I had lots of other ideas just writing this - most of which are not really thought through or even truly usable in 4E. But as I've used up the three things let's just leave it for now.
1) All powers a character has are determined by their class/path/destiny, race and theme. Basic attacks no longer exist and charge is not a combat option. Even opportunity attacks are gone. Instead each character which thematically needs one of the lost attack options can take an appropriately designed power tied to their aforementioned class, race or theme. For any "why can't I do this" situation, the DM is encouraged to use the improvised action section in the DMG.
2) feats are gone. Instead characters get specialisation points regularly - let's say the same progression as feats are now. (Yes I'm just changing names to keep the ideas separate.) Each power has at least one specialisation option which is enabled by allocating a specialisation point to it. As other game rules are forbidden to interact with the specifics of a power, designers can more accurately determine balance for powers and their specialisations. Also characters can choose to truly specialise in their favorite tactic, diversify and spread their improvements, create consistently strong at-will or truly impressive daily's - etc.
3) Magic items add options in the form of new powers only. They have no effect on the attack or damage modifiers of powers other than their own, so the enhancement and item bonuses are gone, necessitating the 'Re-do the combat math' as well.
I had lots of other ideas just writing this - most of which are not really thought through or even truly usable in 4E. But as I've used up the three things let's just leave it for now.