As a Roblox developer, it is currently too hard to make beams with varying widths all the way through the beam.
Currently, beams use two properties to control size: Width0 and Width1. These properties do not allow for full customization of variation in the width of the beam. Using a NumberSequence for size would allow for far more flexibility in using beams.
Since implementing this feature could potentially break a lot of beams, I also suggest an Enum in a property so developers can choose how they want to configure the width of their beams.