In this case, as there is already a system in place that give homosexual couples all the legal rights associated with marriage, and for all practical purposes imbues the same legal status as marriage then I would say that the ideal is Equal Marriage for all, as the practicalities are already in place.
The opportunity here was to legislate a bill that offered Equality...and they fluffed it, creating a inequality to replace a former one. Poor legislation should not be passed simply for political expediency.
so say it takes 2+ years to put through a combined bill and less than 2 years to put through two separate ones achieving the same thing? why choose the combined option?