They have just released the first plugins today, and we've survived (quite comfortably) with Wade without plugins so far :D

You can use Wade for whatever you want, you can even write a physics plugin yourself. But for $15 I think it's worth getting the one by Clockwork Chilli (even if I got it for free as an early adopter :P) that is well integrated with Wade, and you don't have to waste time integrating a different physics engine (let alone writing one from scratch).

I think an alternative that people have used with Wade in the past is box2dweb.