I have limited experience with .50's, but here are a couple of observations:
At only 400 yards, I suppose it would do the job. However, I think it would lose a lot of velocity going to 16", and in turn it's long range capabilities (which is where that rifle and cartridge really shine).
Light weight and very shootable are mutually exclusive with .50BMG
The weight cuts down on the felt recoil.
I have no clue about baffle erosion from that short of a barrel on a suppressed .50BMG. I would
assume it would become an issue, as they usually use fairly long barrels (read; it's still burning powder/gaining velocity at 16"). This is just my best guess, I'm not positive.
Maybe a .458 socom could fit the bill? They are good out of 16" barrels, can be suppressed effectively, have subsonic loads, packs a punch (although only a fraction of .50BMG), cheaper to build and shoot, recoil is similar to a 12ga slug.
Of course, you are free to build what you want with your money. You said it was kinda for shits and giggles, and it would be fun. Just consider the effectiveness of the lower velocity, and that the long range crowd would likely not be there for resale purposes.