I wonder how a low pressure sodium lamp would perform if it took the exact shape as a North American FB40T12U3 or FB40T12U6 fluorescent tube commonly found in 2x2 lay in troffers? For example, how would an Osram Na-T 200W/3 low pressure sodium lamp would behave if it looked like these u-bent fluorescent tubes mentioned above?

What would be the advantages of achieving such a design?

What would be the disadvantages of achieving such a design?

Too complex to make, plus larger outer surface means larger heat losses so lower efficacy.
And it would go against the intention to keep the already big lamps not getting even bigger...
The simple cylinder outer and tge tight arc tube bend make the thing as compact as possible...