Hmm, I thought in the 1.7 version I could change the spawners to EnderDragons. Do you plan to reimplement this or is it off the shelf for good? It doesn't seem to work in 1.8.

Sorry for my late response, I was busy the last weeks.
With spawnEggOverride: true I was able to spawn the enderdragon via an egg and the spawner changed to the EnderDragon, too. (however as expected no dragon spawned naturally)

Oh ok, So you can change it to a EnderDragon but no EnderDragon Spawns... Is there a way to add code that detects what type of spawner it is and then spawn things on a runnable on a for loop that detects how many of those types of creatures are nearby? Perhaps I could code a small add-on for this like "Silk-Spawners EnderDragons" if you don't want to include the code. Then I can use your API to detect if it's a SIlkSpawner Spawner and what type it is.

Technically this would be possible, the addon idea sounds IMO more suitable, however. (I always tried to exclude to modify the spawning algorithm of Minecraft)
Feel free to develop such an addon, if you need API addition/fixes/changes just open a new ticket 👍

One quick question. Are there any other entities that behave similar? If were to code an add-on, I might as well fill in the blanks where SilkSpawners leaves off and design this for the other missing spawns.

Are you able to set the type of the spawner and the mob is just not spawning?
Because I do not modify the spawning algorithm.

You could enable "spawnEggOverride" and then spawn the Enderdragon via an egg however.

Hmmm, It seems no matter what I can't change the spawner-type to EnderDragon. If I use a spawn egg it says "Successfully Changed Spawner Type to RyeDragon" and normal /spawner EnderDragon or other aliases won't work either. (The spawner DOES change types, there's just no mini-dragon icon spinning around in it and it doesn't spawn anything at all) Spawn Eggs do seem to work normally for EnderDragons.
I hadn't seen anyone else report the issue so I thought I had better zip on over to you and let you know. I just checked my config.yml and I do have spawnEggOverride enabled. Here's a copy of my config.yml for you to check out.
http://pastebin.com/ALp7Y4PL
Again, thanks for your help!