I suspect they will be fixed eventually - I can't imagine they will be left "broken" like that for long. (Much like how you used to be able to flaunt a bug in vanilla MC where you could drop a worn out tool and it would be magically repaired!
So, the question is: Should we be using them?
My personal though is that since everyone using the FTB server has the same ability to craft and use them, no player is gaining unfair advantage on any other player if they use them. (unfair advantage is really if a player doesn't have the same access to something that is game changing like that). Much like how everyone has the ability to create a jetpack and fly about.
If you don't want to use them because you think they are too OP and take away a key element of gameplay, that's fine don't use them. There are the longfall boots (that aren't really expensive to craft), which reduce fall damage but not other damage. If you want to use them, I say people should be free to use them... it's not hurting anyone... (literally lol)
You still can cause creepers to explode, damaging property..... and you still receive knockback, which makes battling mobs a little more difficult than if you were completely invincible. So you're still going to want to fortify your buildings and keep things well lit.
Does it take away from the need for diamond armour? absolutely... but with the ability to automatically mine huge areas by plonking down a quarry, and the ability to make diamonds - the value of diamond armour is greatly diminished anyway..... I could craft myself a set for the first time in the entire 2 years I've been playing this game :P
If the people who choose to wear them finding their gameplay enjoyment increased, then surely that's a good thing to let them do it while they can?
Since we're not a PVP server, if someone else has them on and you don't - your game isn't really being negatively impacted upon.... other than if you choose not to wear them, and you fall to your death or get killed by a mob, then you've disadvantaged yourself by not using them. But that's your choice. Surely people should have the choice if they use something like this or not... when it's not hurting anyone else if they do choose to use it.
If we were to ban then, what's to stop people using them when they think nobody will notice anyway? That would be difficult to police.
I say enjoy them while you can (if you want to)....
While it is not perfect, I have found that an iron chestplate has served me well. Up to a personal best of 20 XP levels so far.
I managed to clear out an underground labyrinth in the Twilight and defeat the boss with only the armour pieces I found in the chests there (and no rubber boots) - and even survived long enough to enchant 2 swords!)
There's something very satisifying about risking death to explore something new