Replying to conversation should open a new column
May need a rollup ... but right now it's too easy to confuse replying to a conversation and starting a new conversation. TONS of "new conversations" are little more than replies gone wrong.
Proposal: when you click on a conversation, have another column slide out with the conversation, in the same manner it works when you're in a meeting. IN this way it will be visually obvious where conversations are contained and where new conversations are started.