The XP from Battlegrounds is awful. As Mistahwilshire said above, it's possible to do it but not viable at all. You'll level 10x as fast through questing or instances.
And to answer the questions:
1) Yes the XP was raised, although nerfed shortly after (at the start of MoP I believe, AV was giving almost 1/10th your XP bar for a win at 89-90 -- it then got nerfed because it was the most viable way to level).
2) It'll take months to level a toon from 1-90 through BGs. Even if you win every single BG, it'll still take more time than questing.
Keep in mind OP, you cannot enter battlegrounds until level 10.
-You will be grossly undergeared, unless you're using Heirlooms. Even then, there's a good chance you'll be facing (mostly)
players on the opposite side at the maximum level of the level range. That means they'll have that much more health,
chance to resist and dodge your attacks, and do a lot more damage to you.
-You only get gear from BGing at certain levels. Some of the pvp faction vendors have armor and weapons, but they're
very spread out in level, and also, they're pretty high up when it comes to being available. So assuming you weren't
doing any questing but strict pvping, you'd be grossly outgeared for a very long time.
-The highest exp giving BG, Alterac Valley, won't be available to you until lvl 45. Which is a long time from level 10
if you're doing strictly BGs. Random BGs aren't available until that level as well IIRC, which means that you'll get low
exp from regular ques. The highest exp given are either Random BGs (again, at lvl 45) or any of the "BG Special",
which will have a specific BG give bonus honor and experience.
For a long time you'll only be able to do either Arathi Basin, or Warsong Gulch, (at lvl 30 you can do Eye of the Storm)
and the "BG Special" only lasts about 3 or 4 days. You'd have to do them all day (and be lucky enough to win most of them)
to ever get anywhere. Also, keep in mind that you get the biggest amount of exp for the FIRST win. You get a lesser amount
every other one until it resets the following day.
Just a bit more detail I thought I'd add, but as the above posters have mentioned, its not viable.
What I can recommend though, is to do the "BG Specials" when you see them, and then que for dungeons or quests in the
meantime. Combine them, and you should get a nice mix of pvp to break the pve, and vice versa.
The honor increase should be live today... so it is pretty unlikely that anyone will be able to tell you if the experience was also affected.
Assuming it wasn't, no it is no viable to level via BGs, it is slow, gives no gold and you don't raise your professions. If you want to level fast, save yourself the trouble and buy a second account and link it to your main account.
No. Unless you only play the CTA maps, which seem to give more XP than Randoms do, you will level at such a pace that you'll wonder if you've actually got XP off past 60.