Zaran said:
Do your players actually use this? I don't like the idea of spending life energy to get an extra encounter power. Seems to miss the point of multiclassing. Multiclassing, to me, is to make a character that doesn't fit the mold.
I'm having a bit of trouble parsing what you're saying here.
You don't like the idea of spending healing surges to get an extra encounter power. Fair enough. What would you like to spend to get an extra encounter power? You're going to have to spend
something, and swapping out an existing power is a high price and messes with the role system. There is a price you will have to pay for your extra power. An alternative of handing out "power surges" was discussed, but since 4e rules are extremely gamist and ask you to accept things like second winds and warlord scream-heals, I don't personally feel that healing surges violates the reality of the game any worse than it's already vioalted.

Still, power surges can work fine, as long as the characters have other things to spend them on (perhaps they get X power surges/day, and using a daily or encounter power uses one, so if they use their multiclass encounter power, that's one less encounter power they can use in the next combat...or something). The point is that it be a cost for this rise in power that makes it a risk to use. Multiclassing shouldn't go back to the 2e model of "oh, well, you're just BETTER than a single-classed character."
You also says it "misses the point of multiclassing," but I don't really grok how. The point of multiclassing as I've seen it has always been to blend ability sets. A character in this system has maximum freedom to blend ability sets, with the only limit imposed being that it takes them more effort to blend ability sets then to stick to their own.
And then you say that multiclassing's point is to make a character that doesn't fit the mold. These rules allow you to do that. They just acknowledge that when you don't fit the mold, it is tougher for you. This is both balance-true and narrative-true.
I do think the 3e model of multiclassing was perhaps the Best Rules Evar for multiclassing, but it's not really compatible with 4e's role philosophy. The role philosophy has its strong points (party play, everyone feels useful, there are no especially weak or especially strong classes) that I wouldn't be willing to just toss for a return to a 3e model. I don't think my quick sketchy rules are the endpoint, but they certainly get to the blending of power sets, the freedom to "break the mold" that multiclassing entails.
And I'm interested in hearing what you'd want a character to give up for access to abilities outside of their class that won't gimp the character's role or make them steal someone else's.