My idea is either battle of Singapore or entire Malayan campaing
Starting in 8th of december 1941, Malayan campaing took place, as you probably could tell, in Malaysia, its main goal was to capture Singapore, major Commonwealth city port/fortress. It ended at 15th of february 1942 after the Commonwealth troops capitutaled, led by Lieutenant-General Arthur Percival surrendered to General Yamashita
Both Singapore and Malaya could be a mix of jungle and urban warfare, for example battle of Johor, fighting on the Japanese landings at Singapore island, City outskirts, etc…
The city was defended mostly by Brits, Indians and Australians, but there were also elements of KNIL airforce and squadrons from New Zealand

I would also like to suggest that some squads that served in this theater
55th Infantry Brigade (British)-would be places in TT at SMLE MK III and would unlock Rifleman II, in which it would replace 39th Infantry Regiment, because i think that players should be able to choose if they want Commonwealth or US infantry squad, and as it is rn, the Commonwealth is heavily overlooked by DF
22nd Brigade (Australian)-could be a simple squad for new event, commemorating fall of Singapore

Thank you for reading this, have a nice day