The question of Iron Man 4 will never go away until Robert Downey Jr either signs on or leaves the MCU altogether. There's a good reason for it too: the franchise makes a bucketload of money for Marvel and Disney and RDJ still remains the best-cast member of the Avengers team.
There's obviously also a lot that can be done with sequels, like a resolution to the Ten Rings/Mandarin story without even having to think too far. And age shouldn't come into it either. He looks great still and his action sequences don't even require him to actually do anything: it's a guy in a suit with CGI augmentation: he could literally play the part until he's 80 and not break a sweat.
Obviously, RDJ is also in a position where he can call all of the shots. He will expect a lot of cash, because he knows how much Iron Man 3 made, and how valuable he was to the bottom line on Civil War. He will also be able to add creative input and probably has a say in who he works with.
That's why the issue of Mel Gibson appears to have come up again. Earlier this month, Shane Black confirmed that he thought Downey Jr wanted the former Lethal Weapon star to direct. It was a fairly throw-away comment in a bigger interview, and a lot of sites didn't even pick up on it until now, but it's a strange thing to just throw out there.
Could it be that Black knows something about his two former co-workers? Or is he just being mischievous?
This isn't the first time Gibson's name has come up actually. Back in 2014, when RDJ was publicising The Judge, he spoke to Deadline about the possibility of doing Iron Man 4 saying everything depended on the "half-life of people enjoying the character". Clearly that's not an issue. And then the conversation turned to Mel Gibson:
RDJ: I always say too that if you want to judge a man or a woman then look at their kids. He has the healthiest, happiest, most productive kids you could ever meet or know, and Im fortunate to be friendly with several of them. He did a lot right, and theres stuff he taught me about parenting that didnt sink in at the time but have proven to be true. Were writing this thing right now, YucatanDEADLINE: Thats the project Steve McQueen developed for himself.RDJ: Yes, and Im like, God, if I could find a part for Mel. But he also likes to do his own thing and sometimes he goes out of his way to do the unexpected. Sometimes with these things, it becomes a matter of time, and is seems like its getting a little bit old to hold a grudge.DEADLINE: True, but the year he made Apocalypto, I didnt see a better movie and he was ignored and hasnt directed since. Marvel badly wants Iron Man 4 and youve said you arent doing it. How about the idea youll do that movie if Mel directs it?RDJ: Correct.DEADLINE: Is that our headline?RDJ: Why not? That movie would be bananas.
If you're reading anything serious into that, or Black's comments, you're probably trying too hard. Yes, they're friends, and yes RDJ would like to see Mel Gibson given another chance, but there's no way those comments translate into anything concrete.
Even if Marvel gambled on the Iron Man casting, they won't look at Gibson in the same way. He's an auteur director and doesn't like "formulaic" comic book movies (strike one) and his personal transgressions were not the same breed as Downey Jr's. Self-destruction is one thing, but accusations of bigotry wont' wash with Disney.
So maybe it's time to put that one to bed.