There is a thread in the movie section that says that people really want to see He-man make it to the big screen, don´t know if thats true or not.
It may alienate a part of the fan base as you say... but lets face it´s a MOTU movie in the big screen after more than 20 years, the fans will want see it regardless! And I wont believe that any fan in these boards wont see the movie just because he or she doens´t liked the new design that characters got.
I went to see Transformers 1 and I hated that designs really! That movieverse Megatron was awfull! But what the heck? It´s an all new TF movie I had to see it!