I was thinking the same thing. You hear about combos on different characters (Shaco is the one that comes to mind) with the AA + Tiamat reset dealing insane damage. My thought, which aligns with yours is "hey, you can probably do this on Mundo, and do it well.". With Masochism you can get a double hit the combo would be E + AA + Tiamat (+ Cleaver possibly?), and make them really hurt. However, as I have cycled thoughts with Mundo, my assumption is that it takes a second for Mundo to get to his target. He will most likely be kited by any range champ or caught by cc, which means we would have to completely rebuild him for more movement speed, so we can get the combo off.
Shaco can make this tiamat type combo work since he has that teleport escape/quick entrance. Mundo needs some way to get to the adc faster to make it work IMO, and his Ult falls just shy since it takes away damage from masochism (the catch 22). He relies more on his cleavers, survival, and AOE burn which adds up to ALOT of damage over time. Back in season 2 (i think it was season 2, maybe season 1), I used to get a phantom dancer, blood thurster, and IE and completely tear everyone apart with 2 hits with his masochism + Crit.
I think if we could find a way to make Mundo more mobile, I think this would be a great strategy. Otherwise slow burn is the way to go.