I strongly recommend you do not apply for their super visas at this point in time.
Although the recent rules for Port of Entry admission aren't too clear, it seems like super visa visitors are allowed to stay for up to 2 years only on their initial visit unlike in the past. If your parents are not inclined to/unable to spend up to 2 years in the near future, it would be best to continue with their TRVs until they retire
The retirement would be by next year.