I'm not wrong. Not because such things aren't possible (duh, we have cameras that can do varying frame rates), but because I am aware that content creators contract to deliver a product that will play back properly anywhere. Distributors' deliverables lists specify the exact frame and sample rates that they want, as opposed to what's potentially achievable within the format. Handing them something encoded with variable frame rate is going to result in automatic rejection.

Here's an example of a deliverables manual, from Netflix: http://newworlddistro.com/wp-content/uploads/2013/10/FullTec... You will get something similar from any broadcaster or video distributor. I'm not making careless extrapolations of my knowledge here, but telling you what the industry standards are. I have long involved email conversations about these things with distributors so that stuff I submit to them doesn't get sent back, triggering contractual penalty clauses for late/non-delivery that will make a producer cross with me.