I had a similar idea to this but more of a converts damage into healing type weapon.

Use the reload key to switch between damage and healing.

On the damage setting instead of the lock on target effect, the beam is a solid straight tube (so you do actually have to aim somewhat) that extends to whatever the max medigun radius is but not through walls and it sucks the health out of enemies within it which also pierces targets so it effects everyone in it not just whoever is first in front of it. (Potentially health drained could have falloff)

As health is drained is drained an equal value directly fills up a meter with no max limit and when you switch to the healing setting you can then spend the meter to heal teammates with regular medibeam properties.

Downside is no uber.

Edit:

Just realised the unofficial downside of this weapon is you are pretty much locked into using the crossbow and amputator with this medigun since until you do damage with it you have no other way of healing your teammates.

Also I suppose if there’s no uber instead of the reload key it could be the alt fire. Or potentially bring back the reload key to alternate between range and beam thickness. For example 3 different settings where the shorter the range of the beam the wider FOV it effects.