Given the two-and-a-half decade gap since that movie, it seems like a no-brainer to have Lethal Weapon 5 usher in those now-adult offspring as the new Riggs and Murtaugh, because after all this ...

There Is Still Hope For Lethal Weapon 5 To Be Made Eventually Because Gibson is currently focused on another project, I think Lethal Weapon 5 will remain in developmental hell for a couple more years.