Not happening. Caesar isn't a team player and he's wanted too much by the other Yonko to ever be a productive crew member. The only reason he's even compliant is that his heart is in a lockbox thanks to Law. I'm also pretty sure Luffy hates him, doesn't trust him, and wouldn't want to expose his crew to one of Caeser's betrayals.
Crocodile has a better chance of becoming a Straw Hat than Caeser.
Caesar does have a lot of negatives to his resume and I can't even argue against it. I really think he has some upsides that people tend to overlook.
1. Oda did mention at one point during an interview that the new strawhat would be a past enemy.
2. He can't be an ally member because he has nowhere to go because everyone is after him and his weapons.
3. He has a dream of being the best scientist and surpassing Vegaunk. That's part of the reason why he harms people carelessly.
4. He sort of fits in, shown by a variety of other emotions aside from being a psychopath (embarrassed by chopper, play-fighting with sanji). I can't say the same to other nakama candidates.
5. Caesar could have a potential interest in ancient weapons since he creates his own weapons. Ancient weapons are a huge deal in the entire plot. He also knows the secrets of the SMILE and gas weapons, which is valuable information in the next few arcs.
Overall, his dream of becoming the best scientist was done in a bad way due to bad influences. Let's not forget that robin betrayed many people and didn't care if people died as long as she learned about history and franky stole fortune from luffy and beat up Ussop to build his dream ship. At the end of it all though, luffy saved them and gave them a better way to achieve their dreams, which is something he could do with caesar.