By next year Vlad would have already had experience in AA and AAA (assuming they keep him down all year or until Sept this year). Right now he has a month of AA under his belt. By the start of next season he will have ravaged through the upper minors over a full season already. Totally different scenario.
No one is saying not to call him up in 2019. He's too good and it won't look right (optics) to hold him back until May 2019 when we will be running out Travis, Tulo, Diaz, Solarte, etc, in the infield next year. He should be starting 3b in 2019. But calling him up after a month in AA for a better shot at a 2nd wild card in 2018? When they are having enough problems finding playing time for their existing talent when everyone is healthy? Pass.
Do what the Yankees did with Judge/Sanchez. If the Jays sell at the deadline (i.e. move JD), then consider calling Vlad up then to play 3b for a month or two so he has big league reps before 2019. If the Jays are in it, then chances are they won't be moving anyone from the big league roster, so the log jam that currently exists will still be there. In that case, save whatever days you can from his service clock and buy some vets at the deadline as upgrades. Or if by Aug/Sept he looks like a clear upgrade then call him up then. But now is way too soon.