I think most are still making them atm, but I went on test at the time to find out if I could make my 9 mission opus - The Predatar Taskforce - the way I originally intended as I was crippled by file space among other minor limitations.
Fortunately I have now got around to it and made it exactly as I hoped and envisioned from the initial concept 
Don't know if it 'pushes the boundaries' or is 'groundbreaking' but I aimed to make something more epic than ITF, LRSF, BTF (barracuda or bison - take ya pick lol) and so on. And yes, its true lvl 50 Villain content thats 2 stories that form a single TF when played in one session. I also tried to use mechanics in unusual ways as lets face it we're all in need of a wakeup from the grind. Links in sig.
For me its a case of someone taking the MA and giving us something we don't see or dont expect - basically something that stands out and makes me go woah! There has been a few arcs that do this but none new since i15 that I've come across.
Has anything been published after i15 that really pushes the boundaries of MA?
[b][color=blue]Coldest War /[color=red]/ Omega Patient[/b]
[url="http://www.the-cow.net/"][color=red]The CoW Network (Blog) /[/url][url="http://www.collegeofwar.com/"][color=blue]/ College of War[/url]