Well the choice is to use KOTC's engine and remain stuck with low resolution, Windows-only code and monsters that use a very particular art style; or move forward with another engine. The second option is what I'm doing. Getter77 is right that a RPG is a collection of systems (the main ones being spells, items, scripts, characters, character creation, maps, and combat).
Is there anything planned to distinguish it, or is it more of a clone?
There won't be harvesters or many unit types. Other distinguishing features, a map editor, units that move in formation, and the AI.
Will there be any roleplaying elements to the game and in what world? D and D?
I don't think so.