I am surprised this has never been done given how prevalent the shield and gun combo is in a large number of shooters that shall remain nameless. 
I mean its not like Jackal shields aren’t used in exactly that manner and have been in the game since its inception. Having an additional ablative shield at the sacrifice of mobility could be quite useful. You would just be restricted to one handed weapons and be unable to throw grenades; the grenade button instead locking your shield in place.
Works sorta like the headlight shield. It might be a little overpowered to have a shielded opponent shoot, with a second directional shied.
This is a very good idea
What is this Ghost of Onyx?
Sounds like a cool idea. Like said above if it did come in game it will probably act like the hardlight shield in halo 4