A) Merge WSG and TP into a single battleground called 'Capture the Flag'. Then add another three maps or so, and make it so that when you join CtF it will be on a random map (like arena).
B) Redesign BfG so that it is no longer just a crappy version of AB. I propose that it becomes a reinforcement-based battle, where both teams begin with 50 reinforcements and the objective is to reduce your opponents to zero. Gaining control of the Lighthouse gives you +1 reinforcement every 30 seconds, gaining control of the Mines kills one of your enemy's reinforcements every 30sec, and gaining control of the Waterworks gives your team a +10% damage/healing buff.
C) Scrap Isle of Conquest. It takes too many players for a BG that almost no one enjoys and is mostly Player vs Vehicle, (or Vehicle vs Gate, etc). Alternatively, change it to a world-based BG like Wintergrasp.
D) To encourage more PvP in AV, stick Galvangar and Belinda in the Field of Strife! (Or have some other captains wandering around?) In theory, this would mean that the players would have to clash (instead of zerging past each other) to gain control of the centre, and whichever team does this will have a serious advantage over the opposition. Of course, the main objectives are still in the enemy base, so hopefully this would encourage different strategies as the teams would need to decide whether to try and hold the middle or bypass it, etc. (Complications can be smoothed out by altering the layout slightly.)
E) Using the random BG finder you may deselect one (or maybe two) of the battleground types you do not want to compete in.
F) Add a crap-ton more achievements for World PvP (e.g. getting HKs in every region), and create some PvP objectives in several locations (e.g. bitch-slapping the innkeeper in Goldshire for the Horde). Also, please weaken the city guards and reduce their ability to detect stealth. If anything, have some kind of power-up in some of the buildings that gives the defending players a stealth detection buff if you have to.
Just some passing thoughts...