Just curious, if anyone knows. Are they just account wide? (not battlenet wide)
Logic tells me they would have be account wide only, for the simple reason if a multiboxer (wow 1,2,3,4,5) Ran a dungeon with his toons, he would be locked out of the dungeon after two instances. But I don’t know.
Yes they are Battlenet wide I’ve ran into the instance lockout when doing MoP and WoD LFR chained and tried my second WoW account and I could not enter the instance.
Now if you had a second battle net account that is yours.
You could get around this problem but I don’t know if they would ok with blizzard. 
Wow 1, 2 , 3 etc are all on the same account now, they have been merged.
You were informed of this at the time, many moons ago, so likely forgot.
Did i ask this before, damn im getting old. lol
Also @ kyarlenthaya (wow say that 10 times fast) You can have up to 8 seperate battlenet accounts per person same name ( so 64 accounts in all without breaking TOS)
Wow 8 Separate battle net accounts. 
I remember back in WoD they had the limit set to 3 battle net account for one person.
I had wonder if they had changed that cause I had been seeing some boxers on twitch crazy amounts of characters more then I would ever play lol.
Where did you get this information?