I think it would be pretty cool to be able to unlock a Sherman Firefly with the barrel painted to appear as a short 75mm M3 cannon:
We have one Firefly as a DLC tank with its own unique camouflage pattern in the Normandy Campaign, while we also have a DLC Jumbo Sherman that has its own unique camouflage pattern and sandbags in addition to the free version of the Jumbo. As such, I think it would be possible for the Firefly (similar to the wikipedia links above) to either be unlocked for free out past level 39 or be unlocked with a gold vehicle order from the Logistics tab.
EDIT: The wavy white barrel paint could also be a decal that could be applied to other tanks in addition to just the Firefly. Historically, some crews of the Firefly would paint their barrels as such to reduce the chances of being picked out of the rest of the Shermans as a high priority target. Other crews left it without. Since there are now guys running around with the Conders MG, it wouldnât be too unrealistic to offer the wavy white as an optional decal for tanks.