Chris Highcock of the Electoral Management Board for Scotland suggested this could be an approach Scotland could adopt, and one which would avoid organisational issues—
If the franchise was such that people were registered all over the UK, there might be 30, 40 or 50 ballot boxes and lots of ballot papers, and people would have to get the right one. The obvious approach would seem to be postal voting.vEqualities and Human Rights Committee, Official Report, 7 September 2017, Cols 26-28: http://www.parliament.scot/parliamentarybusiness/report.aspx?