I actually kind of like the idea of bringing back Venom as Brock Jr... here is how I see it...
(For the 5th movie) The symbiote regenerates Brock and expands (that may sound generic, but I'm still thinking as to how it could do this) until Brock is 100% again. But his rejuvinated hatred for Spider-Man makes him power hungry. The symbiote continues to expand until the symbiote grows, and Brock appears to be bulky and muscular while attached to it. He is very grateful to the symbiote, and he feels that he owes everything to it. The symbiote "tells" him that "We are one." Brock constantly thinks "We are one" until it becomes habit, and he is fully attached to the symbiote. He hunts down Parker, and brutalizes him. He tells him "We will finally destroy you! We will finally be rid of you! We are the venom that will kill you! Hey, we like that! We are Venom!" Parker escapes, and Venom plays mind games with him, appearing as Brock to psyche him out. (Think Spider-Man: The Animated Series)
That's all I have so far, it's really just a bare bones idea, but it has enough explaination to keep it in continuity AND please comic fans
(I think)