Sorry to be agressive ...
I love the openSource movement, but I hate stealing ideas from other ...
So I think to make a openSource minecraft clone is a good idea, but please, don't copy this game exactly how it was maked, make a new, with diferent rules, ...( look at Super Mario kart and Super Tux Kart, Super Mario and Super Tux, they have a concept that look the same but diferent )
And make theminimal for being universal, such as keyboard mapping options, or let the player making new block, new rules just with simple text files for example ...
I won't blame you for making a clone, I blam you for copying the notch idea ...