Fractions of EMU could be useful in certain situations if you want to have a more robust way of rounding to an EMU, without the need to change to double for the calculation. Even with EMU we can represent huge document with that still - so we might just sacrifice some of that (upper 16-24bits will almost all the time be 0) to the lower bits. We can adjust the internal representation without breaking the code using this.
As for master unit - I was aware of that and I think we can just change the internal representation to be 1 = 1/2 EMU to support that, but I didn’t want to change the internal representation before I actually have a problem.