Doubt the DMR would be in Halo 4. However.... The chances of having a BR could also be slim.. since it is a new game, and Chief is on a new planet, Chief may not have access to UNSC weapons and who knows what there will be. I could very well be wrong and he could have access to UNSC weapons.
We may very well find the successor to the BR in Halo 4. Who knows. It's all just speculation for now.