I feel like you are jumping the gun a little, if deprecation was announced for Dec 2017 then yeah it would leave give developers some big issues, but right now there’s over 15 months until v3/v5 go away so there’s time to either stick with v5 and wait for Helix and its 3rd party modules to mature, or mix and match both, using v5 only where Helix is lacking functionality and move over to Helix more fully as more endpoints are released.