Things that will be included in the beta (more to come): 

 

• 3D scopes
• Strider (MRAP similar to Ifrit)
• HEMTT (Truck)
• Comanche
• Zafir (future version of the pkm)
• AA Launcher "Titan" (Uses Javlin sighs)
• Green Faction (Greek Army)
• Mi48
• FN2000
• New lighting
• SDV underwater vehicle (the mini-submarine)

 

Things that might be added later to the beta:

• Altis (developer build)
• Stream-friendly UI
• Steamworkshop integration

 

 

Things not included in the beta:

• Static AA/AT
• MBT's (Main Battle Tanks)
• Java support (might be added later)

 

 

Other usefull things to know:

• Q3 2013 is still the aimed release date for ArmA 3
• Beta will be release a few weeks after E3
• Beta content will be first released on the Developer build of the Alpha