Indeed, capitalist levels of productivity are way too low to meet the needs of the majority, they will have to be increased - and happily that should imply the natural corollary, resource efficiency, too.
On Zizek's point, yes, discipline as in alienated discipline over a workforce whose contribution is brute strength will be lost, and a good thing too. Mechanisation should mean there is less need for drudgery, and work can be what it always was potentially, creativity.
Specifically, capitalist only produces goods insofar as they embody value, i.e. that they embody labour power. That means that capitalism has an intrinsic limit to the extent to which it can replace labour by machinery. Socialism would have no such limit.