JesseG88,
This idea is not a new one on in the battletech/mechwarrior history. What your talking about is called Inferno SRM/SSRM's. Infantry have RPG/SRM versions. It is devastating in the right conditions, and can take down even the biggest mechs if hit correctly.
In the older novels with light mechs being struck by these rounds it was almost always a death trap. I think it was the Gray Death saga is when a round explodes on someone's mech and another mech pushes the inflammed mech into the water.. Inferno's put the fear of god into many warriors! Good idea though, and yes these would be awesome, though a balance would need to be made!!