I understand your point about missing a queue for being AFK to handle a pizza timer going off, or having to hit the bathroom, or maybe you're tabbed out to research some tradeskill mats for planning out something for a guildmate. I get that. Here's the situation though.
When a person joins a group to run a normal dungeon instance and tells the group "I need 5-10 minutes to finish something, I'm flying to the nearest flightpoint now" - it's no big deal because the group will wait or whatever. Because it's assumed that everyone has set aside time for the full dungeon run, a commitment will be made, etc.
When a person joins a battleground queue, it's pretty much the same as above. Only now, it's a situation where dropping a queue and just rejoining a few minutes later can be used to rig fights and team sizes, and pretty much you are setting up something where you aren't asking people to wait for you or waste their time for you. Your taking advantage of dropping and re entering the queue is FORCING those people to have their time wasted with the end result.
The server hasn't launched, and we don't have a problem like what I've described on our hands. Yet. But I don't think it's unrealistic to expect it to happen if steps aren't taken to avoid it, and the best step is to simply force a player not to enter the queue at all if they don't have the time to commit to it.
tl dr; be in the BG queue if you currently have the free time to fight in it. drop from the queue if you don't.