I thought about it when I upgraded the SSD in the Ally, but decided against it considering it was still early days back then and Asus hadn't released all the drivers yet.
I don't think you'd face any issues as long as you install the MyAsus app and keep all your drivers up-to-date.
That said I don't think it would have a noticeable impact on performance either, just the benefit of a smaller storage footprint.
