I would say yes. Why wouldn't there be an enrolment period every year? That's certainly one approach. The 12-month probation period is quite a lengthy one, in any case. Does it always have to be 12 months? I understand that for maternity benefits one may suggest that 12 months is the proper period to prevent what would be called anti-selection. On the other hand, that hearkens back to--I don't know if you remember--what used to be called the “magic 10” rule, under which women had to be in the labour force between the thirtieth and the fiftieth week before the child was born. That was abandoned in the mid-1980s. This sort of reintroduces that measure, but for self-employed workers only.
On December 10th, 2009. See this statement in context.