AbdulAlhazred
Legend
The less the game siloes, the harder it becomes to design a game around this sort of presupposition.
Hmmmmm, not sure this is necessarily true. Could be a point of further discussion.
I'm not saying that Rolemaster is the be-all and end-all of diminishing returns as a design approach - but I think that 4e's more explicit siloing, based on a clear conception of the place of combat in the game, does a better job at supporting, out of the box, coherent party design, coherent encounter design, and coherent play.
Something closer to 4e's design, that I think someone mentioned upthread or one of the other related threads, would be to replace Feats and Utility powers with skill powers - so use skills as the starting point for siloing. And then think about what mechanic you use to require every PC to at least have some modicum of ability in each skill area (perhaps using stats to help characterise the areas - STR, DEX, CON, WIS for "exploration", INT for "knowledge", CHA for "social").
4e accomplished this last point pretty easily, just add 1/2 level to every skill and focus pretty much all task resolution on skills (and combat is really just a slightly more elaborated variation of the opposed check mechanic).
So, the issue with 4e is simply that because the game is focused around the combat activity to organize character concept/role you are motivated to add to your combat capability, but I'm not sure actually that this is a truth that must be absolute. Certainly if you used Diminishing Returns it would still be TRUE, but the two things would offset each other if it were properly implemented.
My motivation here is that hard siloing with keywords or explicit siloes of any sort is a 'big stick' approach. In some ways it is NICE that you can't be a useless lump in combat, but is that really so vital it has to be forced? I'd think the better approach would be to make it the easy way to do things, and provide good strong build support so you can simply start with a workable character and customize if you want. Something similar to an E-class character, then if you REALLY want a wallflower you can craft one.