I'm not sure I understand this, but it appears to me that the consequence would be a reversal of defaults. Now we assume that a sequence of commands is the default and parallelism has to be explicit. He proposes to make parallelism the default and sequence explicit.

My question would be, is parallelism really the more frequent case? I mean if we take all the instructions in a program and analyse which ones are just accidentially sequential and which ones have to be sequential to be correct, would we have more parallel pairs or more squential pairs of instructions?

I believe we have more sequential pairs and that it'd be very cumbersome to default to parallelism. But there may be special cases where defaulting to parallelism is beneficial.