We used custom selects in the previous version of XStore before the 5.0 (fancy select) but we removed this additional custom script to speed up the theme. I’ll pass your suggestion to our developers and I will also ask to add maybe some option to allow users to enable custom selects and inform them that it may slow down the site a little bit because uses the additional script.
I have sent your request to our developers but they have not confirmed that they will implement this in next update yet. The meeting and discussion about new theme options should be at the end of the month as I know. Once I get any new information about this I’ll inform you.