Gah! Why is that every forum I've been to lately keeps proving to me just how stupid people are. There is nothing on earth wrong with cosplaying from series that are ending or that have ended. That shouldn't even be a factor in your decision if you like the character enough to want to make a costume in the first place.
Conventions 2014: Costume Con, Superman Celebration, Project Comic Con. (Others TBD)
Working on: Air Nomads- Lion Turtle City of Air-LoK, Lily Potter- HP, Fire Lord Zuko- Older version-AtLA