It would be really cool if there were a screen similar to the lightsaber hilt selection screen for other weapons. All the hard coded cosmetic gun differences between models should be player choice. Might as well allow players to choose between the 3 different frag grenade models too. Perhaps even allow the player to choose color for specific guns (pistols could be red/green/yellow, bowcaster could be red/green). It's not any less immersive than Luke running around with two purple blade Desann hilts.
Only issue would be some guns currently have visual differences based on what abilities the player has (M5 model changes with sniper/grenade attachment, P3 has a different colored nozzle, clone rifle has 3 different models depending on level and if you have blobs), but I don't think it would be a big deal to lose that. In every case except CR3 no blobs the model difference is very subtle and hardly noticeable. You can even hide the P3 model difference currently by playing Kyle who always has a Bryar at any level.