We'll have to wait and see how it turns out. Buying a 4:3 version is a bit different, because you are obviously losing out. It'd be more like buying a colourised version. I can understand purists not doing that, but for me it will depend on how good the treatment is. Possibly films intended for 2D will be better in 3D than ones actually intended for 3D, because there should be fewer gimmicky uses. Or maybe it will be rubbish.
In 5 years time 3D will be standard on new TVs, much as HD is today. I know it's a bit off-topic for this thread, but when considering whether to re-buy in Blu-Ray it's worth bearing in mind.
It turns out to be pretty easy to do, nowadays. The main technology is based on a screen with a very high refresh rate, which they can do now and which is a good thing to have anyway. You also need high bandwidth from the device to the TV, which modern HDMI can handle. The rest is pretty trivial.
You'll need glasses, which use battery-driven shutters rather than polarisation - it's a different technology to movies. (Cinemas use double resolution rather than double refresh.) These will cost a few pounRAB to make, but overall it'll be cheaper to make only 3D TVs than a mix of 2D and 3D.
The glasses are a drawback, but you only need them when 3D is enabled; the result of the time it'll function like a 2D TV. Avatar and other recent films show there is enough interest. It'll happen because of economies of scale, even if some consumers don't like it.