You want burns on primaries? How about this method!?
A simple upgrade node on every legendary primary. It requires glimmer and an "Elemental Pack" (either Solar, Void, or Arc). When you buy the upgrade, it's not permanent. The more you fire the weapon, the upgrade node slowly depletes until it reverts back to Kinetic damage. At this point, you can now choose another upgrade pack to apply to your weapon and so on.