Don't know how to do the spoiler thing.
It won't be Carnage for a number of reasons:
1. He's more Venom's enemy than Spiderman's so they'd have to twist his story a little.
2. The symbiote may still be alive but Eddie Brock, the physical human being, is dead. Gone.
3. Sam Raimi HATES Venom, why? "Lack of Humanity", so what are the chances of homicidal maniac being in the next film? You do the math.
They're facts. These are my opninions:
1. Lizard is a shit enemy.
2. All other Spiderman's enemies are shit. They've used all the good ones and killed them off too.
3. In reply to zeon9881, Harry is dead, he won't be returning.
There was other stuff that I wanted to write but I can't be arsed. I'll probably something else once someone says something which is complete bullshit, it always happens.