On May 29, a new playable faction will be added to Rising Storm 2: Vietnam from Tripwire Interactive. The update, codenamed "Army of the Republic of Vietnam (ARVN)" will add in the new faction, new weapons, and five new maps.
Over one million Vietnamese served in the ARVN over the course of the Vietnam War, with over 250,000 lost in action. Largely equipped with older US military equipment and trained by foreign military advisors, ARVN soldiers bore the brunt of frontline fighting throughout the war both prior to the escalation of US military involvement and after the US began reducing its troop presence.

Army of the Republic of Vietnam (ARVN) Weapons: New Army of the Republic of Vietnam (ARVN) Maps: Quang Tri:A Sau: Set on an airfield and fortified camp in the A Sau valley, this nighttime territory attack map finds ARVN forces defending against attacking NVA main-force units. Visibility is limited under the cover of darkness with occasional flares lighting up the battlefield.

New Community Maps: RISING STORM 2: VIETNAM $40,000 Modding ContestFirebase Georgina:Borderwatch:Resort: US Marines stage a heliborne assault from the sea on a resort area held by Viet Cong guerrillas.

I'm going to assume the game will have a free weekend and/or discount when this update is released. That seems to be what happens on these sorts of updates. That's just my guess though.