I can't tell you what equipment will be used by police in the future, but I can give a (partial) list of modern items that may be relevant to play
(Quick list below from current experience as SRT member, less lethal instructor for local PD, training officer for patrol; military, corrections, and law enforcement experience)
On Patrolman: Handgun, club, body armor, communication device, pepper/oc spray, flashlight, cuffs. Varies greatly depending on if you encounter a conservative cop or a "Rambo". Other misc items possible: backup handgun, knife, utility tool.
In Patrol vehicle: shotgun, possibly auto. rifle, vehicle radio, possibly a computer, something to stop a vehicle (stop sticks), GPS device, cage for prisoners, maybe a dog, possibly less lethal weapons (see below)
Riot Equipment: Heavier armor, helmet w/shield, always less lethal weapons, longer club, riot shield, grenade launcher (for chemicals not explosives), chemical sprayer, chemical grenades (smoke or less lethal).
SRT Equipment (SWAT): Heaviest armor, helmet, SMG, auto rifle, sniper rifle, handgun, fire ext., battering ram, night vision, less lethal weapons including various grenades, first aid kit, grenade launcher, all depending on duty position in the team.
Detective/Investigator: Handgun, body armor, communication device, cuffs. See patrol vehicle for items in a vehicle. On-person items may vary considerably with some being equipped as well as a patrolman, others only a handgun and radio.
Less Lethal List(not less then lethal some of these can still kill): Pepper/OC spray, rubber or wood batons shot from various weapons, bean bags shot from various weapons, pepper spray shot from weapons, taser and other electronic stunners, extreme light devices which blind, various grenades including chemicals such as pepper spray and area of effect rubber batons which can be hand thrown or shot from a grenade launcher or shotgun with attached launching cup (kind of like a ram grenade).
I think the best bet for a future police weapon is one that can instantly switch between various levels of force, from less lethal stunning for the irrate customer at the mall to a kill shot for when the local mercenary in combat armor has drank too much.