I would assume at some point Aatrix won't work.  I haven't seen anything to say that is the case.

Remember that Sage support won't assist with issues.  As a reseller, I know most of the things I call Sage for are software bugs so that's not a major deal for most items.   With payroll being so time sensitive, I won't feel comfortable with being on a version that Sage doesn't supports.

What will your clients do when their operating systems are no longer supported on v2017?  That will probably happen in the next 2-3 years.  If your clients continue to use Sage, they're going to have to upgrade at some point.  Might as well upgrade now and be on a supported version.