This will "solve" the tank shortage for a few weeks, but that is it.
What will it do? It will compound the biggest problem in WoW - poor player behavior. You will have poorly performing tanks who will take massive amounts of abuse, and pro tanks who will abuse the casual dps player (you know the guy - the hunter with +intellect enchants).
As Big Bear Butt says - it's haggling over the price. And it's not a solution.
There are a few solutions - most involve re-thinking the LFD tool. So lets take a look at the tool first.
What does it do well? It is great for leveling dungeons. It was great in Wotlk with the easily out-geared heroics (and relatively simple mechanics). It lets a solo casual player get involved and do something. Where does it fail? Clearly, in Cata Heroics. After the initial shock, they aren't really that hard. But it is totally possible to still wipe - a silenced healer on Ozruk, someone failing at beams in BRC, etc.
I have a tank alt, and I did maybe 10 heroics. Just enough to get a few pieces i need. Rest was all purchased, and I'm raid ready. I only do heroics if it's a near-full guild group. Why? Accountability.
Alright alright, we all know the pros and cons of the LFD tool. And we all dread using it. Hardcore or Casual, you hate the (very good) chance of running with a group that ruins your enjoyment. Sometimes you don't even realize you are doing the same thing to others that you dread being done to yourself.
So what are the solutions?
NOTE: keep in mind that I'm a fan of hard content - the solutions below are simply to encourage the mass amounts of casual players into taking on a role of tanking, or at the minimum finding a way to have fun in a short time.
Solution 1: Separate full Random Heroics from full pre-made group Heroics.
Blizzard wanted Cata heroics to be more challenging than Wotlk. And they are (were?). The problem is - a full guild group (from a guild that raids) already are chain pulling, ignoring cc, and generally blasting through heroics. Take one or two of those players, and put them in LFD, and they double or triple the length of the heroic, might wipe, and generally get frustrated.
So tune the full random group heroic appropriately. Doubling the content would be best - but even taking the same dungeons and removing the more difficult fights, while appropriately adjusting the rewards, makes a lot of sense.
The casual PvE player wants to log in and do something in under an hour. Give him this opportunity. Harder core players are happy, and the casual is happy. Think of those LOTRO Skirmishes - they are great for a quick pickup group with friends.
Solution 2: Change LFD groups to have 1 Tank, 4 DPS, 1 Healer.
I know, crazy talk. But again LOTRO does it. It might not even need a tuning change - sure you compete with one more person for that sexy i346 loot you so desperately need - but this instantly reduces queue times for DPS.
Solution 3: Give tanks Snap Aggro
A huge problem in LFDs is DPS who refuse to "target skull" (or assist the tank). They randomly target whatever they want, and start up with the bad behavior if they pull. Tanks have to work harder to compensate for the lazy DPS, reducing the likelihood of queuing again.
In addition, the vengeance mechanic doesn't scale well in heroics, though it works very well in raids. So you have a tank fully gemmed/enchanted for mastery, with occasional aggro problems in heroics. I personally didn't find this - but I see it happening a lot.
TL:DR; Make tank threat easier for the casual tank.
Solution 4: Accountability
Sure you can ignore that frustrating DPS doing 3k and going AFK constantly. But you'll see another one just like him. Kick him? Well the chain-running tank doesn't like doing this - it hurts their ability to kick someone later in the same play session. I'm also not for the idea of giving tanks true leadership over LFDs either - reasons why are well documented elsewhere.
So how can you do this? One idea I had read somewhere was to have a like/dislike option on players. Rank us. If we maintain a "high favor", give us a reward. Use the pets and mounts for this. And don't just add up likes/dislikes - factor them by the player assigning it. (ie, that jerk player who has a low ranking assigning "dislike" to everyone is automatically not considered much). There are many systems out there for this.
Solution 5: Create a "Trusted Group of Guilds" feature
Often players in LFD behave very poorly when alone, but this behavior doesn't exist when in a guild group. This is for Accountability (see Solution 4). So allow for cross-server guild alliances - the LFD tool searches this pool first. This idea isn't that well thought out however, as small guilds and solo players would be left out.
Solution 6: Consider Alternatives for Random Heroics
This is a bit of an extension of Solution 1. The LOTRO skirmishes were a great way to quickly get together with friends regardless of role (tank/healer/dps) and have a bit of PvE fun. So create/modify content for this. Call it "Stonecore Skirmish" - mini-bosses, trash, and no requirement for specific roles in a specific balance. Most classes can self heal enough to carry them through...and it makes CC important too because honestly preventing damage taken is the same thing as healing. Have the mini-bosses drop i333 loot, with the final boss dropping one i346 piece (or something like this).
The LFD tool was a great solution for getting groups together fast. It's broken now - killed ultimately by heroics that have mechanics that generally must be followed. In Wotlk, most random heroics took 10-15 minutes, now we are seeing people stuck for sometimes 2 hours to complete one heroic, including queue time.
Something must be done - and the bribery is not a real solution.