You are free to stay on FPP v5.x for as long as you want. You won’t have access to DPIPixels, bug fixes, or other enhancements, but as the saying goes “if it ain’t broke, don’t fix it.” We can not guarantee that there will not be changes in FPP Connect that break older versions as we do not test older versions and instead focus our development and testing on the latest FPP version.