That is friggen pimp... I want a Beast Master... I'd name him Dar.
Anywho, I for one think the biodome should be kept in, at least until we have some other way of spawning units post 'the map is filled with countries' game play. And did you ever get around to expanding it to be able to spawn any subdued animal, or just the 4? (Or 3? I forget).
And I would like to make 1 more point: Diversity of units should _NOT_ be for the sake of being able to make more powerful units, they should be for the sake of diversity. So each play through could be different and have different options depending upon the starting resources of your country. At pre-Monarchy you don't have to many cities, up to say 10? I forget. So hopefully each play through would be different depending upon which special resources you get. At least, in my opinion, that would be full of awesomeness. Yo.
Edit: Also, you could make the Panthers like the Wolves where in you have to make a special building by consuming the Panthera (Dog Kennel) to be able to build the Panther/Lions War units. That way, if people don't want to, they don't have to 'use' one of them to make it. So for small map'ed games this would make them pick and choose what they want or don't want since animal units are semi-scarce.