See, you say redcliff is habitable, but i've been there and it's clearly not the same town... or i choose to believe it's not, because otherwise it makes no damned sense 
Everyone is taking my comments to mean the taint is 100% contagious and 100% lethal, but i never said that.
Oh Redcliff may have been wrecked, but the land isn't tainted. The whole area can still support life, unlike say the Western Approach which is finally starting to recover.
As for 100% percent lethal, that's pretty much the Taint in a nutshell. It either kills you or renders you mindless.
I'm not sure if you played Mask of the Betrayer, but if you have, you're familiar with the spirit meter mechanic. The Taint as a game mechanic would probably get similar wailing and gnashing of teeth.
Conceptually, the meter was a neat idea, but I know a number of posters over at Obsidian's boards back then ended up saying they just dev consoled it because the mechanic was cumbersome.
Realmzmaster also makes some good points about using a random mechanic for the Taint. Spending time getting attached to an NPC just to have him sicken and die on a dice roll might work for tabletop, but for a crpg, not so much.
That and reducing it to a random mechanic cheapens it. Death by Taint is a horrible thing, and even worse is becoming something like Ruck. You can't play that kind of drama even with the computational power and programming advances since 2009. To make a real impact, this kind of thing has to be scripted. Playing out as story. To do anything else cheapens it.
I can understand wanting more of a threat, but at the same time, reducing it to a random mechanic opens a whole host of new problems for both Bioware and the gamer.