I personally think that most of the Unit promotion events should just be retooled for different units as much as is possible, the list clearly shows some like shock, cover, flanking which will need to change. I did not post the amount of active events, but some of these events are considerably more common than others. Some on these lists are not even activated in game. It would be unwise to give promotions like commando without making the event occur ad a rate less frequent proportional to it's advantage or adding another requirement, perhaps even making such a bonus, a product of a quest.
Actually I really like that last idea, a commando quest. What would be a good mission for such a quest? We could do this in addition to an event to give commando status to the units you mentioned.
Something occurred to me, we can use the events system to trigger world projects whereby, like the space ship, components need to be built in multiple locations. Just a suggestion to throw out there.
Another idea is perhaps changing the nature of obsolete promotions. I am pretty sure this is an XML thing.