I don't think a real roadmap would work for Scirra because of the way they rapid fire releases. Instead of saving up features and then being like here's version 100 with this.
The best thing they could come up with (which I think I saw somewhere before) is just a list of features that they are going to be adding in the future, in no particular order.
Personally I like the unexpected emails saying "Hey new feature here!" instead of the waiting continually for the roadmap marker to be hit.