A fan-made random map generator for Heroes 5 has appeared: Tapani's HOMM V Random Map Generator (the author of the generator is Tapani Utriainen). According to the author himself, generating large maps takes a lot of time and requires a powerful computer for good performance. You can read about all the settings in the attached file readme.txt. The only drawback of the editor is that it generates maps only for 2 players, but this is version 0.7, and perhaps the final version will have more features; moreover, by that time, an official editor will also be available, which will be included in the add-on Heroes 5: Hammers of Fate, which will appear very soon.