How to get people to tank!

[Makeda]

Or you can change the content to accommodate the imbalance better.
Or you can make content that doesn't rely on the roles - it's not that hard, you only need to replace unavoidable damage with mechanics.

Do note that Guild Wars 2 started out this way, and when it launched an expansion... it put tanking and healing roles into the game, and discontinued development for its 'dungeon system' that has role-free group content.

It just wasn't working.

One common problem seen when you make it so content doesn't NEED a tank or a healer is that groups start refusing to allow tanks or healers to come. City of Heroes is a case in point here - mobs got easy enough to deal with when bringing 'support' roles - buffers and debuffers... and so tanks, healers, and pure DPS all ended up being disinvited to a lot of 'speed runs'. Guild Wars 1 makes another point. You could bring an NPC healer that was 'just acceptable enough' to keep a group barely alive... so player healers got disinvited so as to avoid the risk of a player who wasn't perfect. People preferred a flawed but viable "bot" over the risk of an unknown.

And Guild Wars 2 again makes the extreme example. People learned that they could speed farm content with 'glass cannon' DPS builds - characters that could barely survive any damage at all, but fast players could out dodge/run attacks... so anyone not on a glass cannon DPS build... was told to not show up...

- And that led the developers to make content that needed traditional tanks and healers (Though in GW2 raids, the same character can be both the tank and the healer at the same time).

Trying to get people to tank...and especially forcing people to tank in the way the OP suggests IMO doesn't lead anywhere.

People either like being the center of attention or they don't.

You can't use gimmicks to change this or trick people into liking it.

This is just a fatal problem of anything based around teamwork. Most people do NOT want to be the quarterback, tank, lead vocalist, public speaker, point man, etc... But anything involving teamwork needs someone to step up and do that task. Not so much a leader per se - but a focus for the attention at the least.