I think it's related to one bug more than a feature request. One example for all cases:
Player is writing message in the chat tab and someone starts to trade with him, or an other window appears or changes it's focus over the chat window and player doesn't recognize that until he types some more letters. Unfortunately, that causes he starts to use shortcuts and he either accidentally accepts or declines the trade, opens assigned windows, starts to run, casting or whatever is assigned to the used keys. I think everybody knows what I am talking about. The behavior should be that the new window appear or the windows change their contents but the originally selected and used window should stay selected and used.
If it is just about tabs in the chat window, then it's caused by selected option "Default last chat" in Options - Interface - Chat. That way you will always use the tab selected instead of last used, unless you will specify the other tab with command, i.e. /say or /tell.
About the interface - it's possible to make the chat window have the tabs on the top (as it was in 0.4) instead of on the left side, which is IMHO much better, because then you don't need to have too big chat window to see all tabs. If anybody interested, I can post modified xml file for chat window.