This looks incredibly promising, and from somebody who has witnessed a friend try to re-create a map editor from scratch in XNA I bet there's a lot of work that has been put into this already. I really like the fact that this works through C#. I've only just recently learnt C# language and even more recently familiarised myself with XNA - therefore I know how powerful it can be!
I do have a question, however: what are your plans with regards to functions the future game developers will have once this engine is released? Rudimentary functions such as adding NPC's, giving Pokemon, giving items, etc. are expected but to which detail are you looking to giving default functions and actions for the developer to use? A planned list will be nice, and some people who are prominent at XNA could even help you to write them up, allowing for a quicker build overall. I do believe that the more functions you add, the merrier!
P.S. That map editor looks beautiful!