An ideal Focus/Rage single-target parse has Master Strike/Ravage at about 15.7% of total damage dealt. The spec is just over 9% behind the other two specs in terms of single-target damage. We don't want to buff AoE burst, and we don't want to buff reliable single-target burst since that would raise significant issues in PvP. If anything, we want to incentivize a slightly longer average delay on Force Sweep/Smash (situationally).
What if Force Sweep/Smash had a 25% chance to finish the cooldown on Master Strike/Ravage? If it were a 100% chance, then Master Strike/Ravage could be used 233% more frequently than it is now, which is a damage buff of almost 36%. However, 36/4 = 9, which is about what we're looking for. Thus, inject a bit of RNG into the Focus/Rage rotation and you've got a roughly balanced buff. Note that this increases single-target damage tremendously while simultaneously delaying Force Sweep/Smash slightly (on average, less than 0.5s per Force Sweep) and not increasing AoE burst.
The downsides of course are a) it's unreliable, and b) it happens with a low enough proc rate that you will frequently find yourself in danger of stepping on the natural CD for Master Strike, which incentivizes putting Master Strike ahead of Force Sweep and thus delaying the smash even further, which seems like a significant reorganization of priorities. A simpler solution might be to simply lower the CD on Master Strike/Ravage in Shi-cho form, gated by a talent high in the tree.
master strike is actually a pretty minimal increase for focus due to the fact that focus almost never runs out of rage and master strike doesn't reduce the cd on sweep, zealous leap. so, each time you master strike, you effectively increase the cd of the next sweep by 2 seconds, which offsets some the gain you would get from using it instead of slash. example, my vicious slash does around 2600 including force lash, my ravage does around 6800. so you gain 1600 damage from doing ravage. However my smash does 8.3k fully buffed. Since the cd is 8-9 sec Increasing the cd by 2, decreases by dps of smash in that time by around 20%, or in this case around 1600. The numbers aren't exact, but close enough to show that ravage is a very minimal increase in dps for rage spec and is more used in the rare case you are out of rage and battering assault and berserk are on cd.