The idea is a command that allows you to pause a sample that’s playing and in turn have the ability unpause it.
This would help with effects like manually gating, time stretch effects, vocal samples, etc.
I suggest adding a new code to the backwards command, e.g. 0B02 for the effect column and B2 for the note column.
What’s the difference between this and just using an OFF row and then starting back up with an 09xx command to start where you want?
YES! No more looping back and forth a silent section with b00/b01 
The difference is that the exact position where you stopped playback can not be reached in 99% of the cases with the 9xx command (which is actually why it’s called that way).
It saves you from needing to enter the 9xx codes and like Johann said, you avoid the inaccuracy of 9xx.
+1. And an implementation thought: would the sample be “stopped” (as if it had been really stopped, with the amplitude going zero), or “paused” (with the amplitude staying wherever it was when the command was hit)? I guess if it were “paused”, it would be nicer for timestretch effects and the like, but there could be DC offset problems.
Yes, lets have to look up an offset every time we want to introduce a gap in a sample playback… that sounds extraordinarily fun. As an added bonus, the offset will be incorrect 90% of the time! 
+1