Fortify's CD isn't particularly short, and two carries and three tanks will take a while to knock down towers, while if the enemy keeps hammering, they'll burn through your Fortifies and then be able to take you down a lot faster than you can counter. A well balanced team will be able to mitigate yours in a team fight, and I can't help feeling that against anyone who know's what they're doing, you'll just die a slow death.

I was just thinking about something sort of along these lines. The basic idea is to make a team that can play very effective tower defense, then have 1 or 2 quick pusher/tower-smashers to force a different dynamic than the 5v5 dynamic that the other team is presumably set up for. Fortify, mobility, pushing, towersmashing, and champs that can play effectively around your towers (on def) are key. You can keep 3 or 4 to defend your tower as needed, and then have 1 or 2 rushing around the map slapping towers...or quickly losing/taking the opposition if they split off a force to get you. The key questions are, "Can you have 2 people push down towers unopposed faster than your opponents can push down your tower being defended 3v5?" and, "Can you force them to fight in smaller skirmishes that you are built for, instead of the 5v5 that they are built for?"

Champs that I think could be rolled into such a team are:

Singe, Evelynn, Udyr, Zilean, Rammus, Yi, Sivir, TF (Singed and Rammus have great mobility and play great around your turrets)...
Maybe an Alistair and/or Soraka on the defense team.

I'm just curious if this sort of approach could be viable in high-end play.

I don't think 5 Fortifies is viable in high-end and here is why.

If both teams are playing tight, you will hit the end game.

When you hit the end game, you may have them pushed, but they have 5 more versatile summoner skills than you that will improve their ability to gank you.

Fortify as it is right now is only decent when specced into defense, to take out minion waves. You will need aoe damage to wipe the minion waves to make the invulnerable towers click on the heroes so they dont stand around waiting for you to blow your fortifies. And not all champs are viable with Defensive Specced Masteries.

If they out push you, and count your fortifies, they will be likely able to make all of your fortifies go on cooldown, and then proceed to push the tower hard.

Rammus is a must if you try this, as the enemy team will eventually ignore you and do whatever they have to, to drop a tower. You need them to target you to start taking damage if and when all forts are down.

Lol. I'd try it with you. I think the tower defense team could be very deadly, too, and keep them from wanting to attack. Put a Blitz and a Rammus by the tower, along with some stunners, and they really won't want to come close. The idea on defense, imho, wouldn't be to just stall, but to be able to kill anyone who comes near your towers, esp with the consistency of fortifies available. When you kill some on defense, that defense team quickly becomes another pushing team. Wouldn't hurt to have a smite or two to smitesteal if they attempt baron...or some other solid reactive strategy for when they go baron.

I'd try it =P I'll go Ryze.