Hi Tug Fanatic, if I understand correctly you wish to remove the shaft from your brushless motor and fit the prop shaft inner straight into the motor?
In theory I suppose it's a good idea, in fact if nothing goes wrong then it should be quite alright. Remember though that if you need to remove the motor you will need access. If this is achieved by releasing and sliding the shaft out of the motor that when you come to put it back in you will have to push it back up through a grease filled outer shaft first. If the motor is fitted close to the outer shaft to save space then you may not have a lot of space to get fingers cloths etc in to degrease it. If it isn't fitted close then why bother in the first place?
As for alignment, well if you connect the motor to the shaft with a shaft adaptor (the brass tube type with the two grub screws) then this will also create a straight fit and be easier to access the motor.
Also the length of the inner shaft would have to be longer than the one supplied so you would have to buy a new shaft.
It doesn't mean it can't be done (I think, maybe I've missed something too!) See what the others suggest. U2