8/9 speed cassette spacing is 4-5 mm. Chainrings are what, around 7mm? So, if you can shift a cassette fully at 4-5 mm, a 2mm chainline differential and a 3 mm flex in the same direction adds up to a dropped chain.

The biggest concern is that the flexing and dropping of a chain due to ramped chain rings and cogs will happen at the most inopportune time, being hi torque. A quick out of the seat sprint, or climbing a hill is not when you want to lose a chain.

Then there is the variable of using a chain tensioner.....