Boss fight idea

I was thinking about Yoshi-p's post about roaming NM that got stronger as we killed it. What do think about this idea about a NM who gains levels as we all do. Either make the exp gained be a fixed timer(i.e. 1 month), a fixed amount of deaths or a player kill counter. It would make things pretty interesting if the entire strategy changed(kite, tank and spank, lag cracks) and you would need to learn a new way to kill him but that's a lot of work. So to simplify it how about just gaining a new move or multiple moves to change the strategy a bit. What do you think?