It is probably the intent of the Constitution that the Speaker should be a member of the House. After all, how can you speak for the House without being a member of it? There is also a strong historical precedent that indicates that the Speaker of the House must be a member of that body before he is elected. Never in US history has the House even attempted, so far as I know, to elect a Speaker who is not a member of the House. In fact, not only has the House never elected a non-Representative to be the Speaker of the House, none of the original 13 colonies legislatures, nor any of the 50 states, so far as I know, ever elected a speaker who was not also a member of the chamber who elected them; also the the Speaker of the British parliament's House of Commons, from whom our government in a large part derives is always a member of the House of Commons. There is absolutely no reason or precedent that suggests that the Speaker of the House can be someone who is not already a member of the House of Representatives.
However, that being said, it is true that the constitution does not explicitly say that the Speaker of the House must be a member of the House of Representatives at the time of his election, so I suppose according to the letter of the law the House could try to choose a non-member to be their Speaker if it wanted to. After all, it is the House who is given the sole power to "chuse (sic) its Speaker and other Officers." However, doing this would violate convention and parliamentary tradition.
Thank you very much for the very thorough explanation and bit of history! If either House ever has a job opening for a Parliamentarian, you should sign up and apply! Feel free to use me as a reference. :p
The Majority leader could serve the same function as the Speaker, except as presider. I like the House of Commons idea. Let the Speaker be neutral. however. In the steering committee, the Majority leader might have two votes, but not five. Let the conference have a real decision.