Warning - Don't Use The Extended Edition Editor If You Want Backward Compatibility!
Reason #0
If you make your maps in the ORIGINAL AOM / Titans it will work for Extended Edition. BUT if you save your old map in Extended Edition you break your map forever from being played in the original!
Reason #1
People who have original AOM / Titans and online communities such as Voobly still play the original and won't be able to use your maps.
Reason #2
Original Age of Mythology Runs Better On Older Computers.
30fps Extended Edition Low Settings VS. 60fps Original High Settings.
Why lose frames for no reason?
(YES, you can run the original in Hi-Definition without any problems with one or two tweaks! The ONLY reason right now to play the new version is if you want to play online with the Steam Community)
Prologue
They might be coming out with an expansion for Age of Mythology Extended Edition.
When this happens I can see a lot of people transitioning to the new version but that still doesn't give me a good reason to BREAK backward compatibility of scenarios right now because you can always save your maps to Extended at any time but you can't reverse this process!
One thing I notice that tricked me into using the Extended Edition Editor was the hi-definition support. But then I realized with a simple modification you can use the original editor in hi-definition too. Here is a link to the simple modification.
http://aom.heavengames.com/downloads/showfile.php?fileid=11076