Gaining BP for militia has been previously mentioned in the ideas section, and never passed. It's difficult to justify gaining BP from them since they contain no farm space consumption, and even if conceded; would still make them annoying. People also argued too much over just how much BP you could gain, ranging from every second to every tenth militia killed.
Enlisting militia can hardly be considered a tactic, it should be more accurately described as a free means to gain DBP and damage the attackers troops, which already have lower values than defensive troops have defensive values (add in wall, tower, research, spells, biremes, etc...)
Militia should be a last-ditch defense, not something you can bring out every few hours at the click of a button. Having the added difficulty of training them is actually a decent idea since it prevents the current abusive use of them, requiring a bit more activity to consistently bring them out, or relying on other means to protect your cities.