Since March 2015, Barnawi has appeared in several videos distributed by Boko Haram, claiming responsibility for successive attacks, earning him the reputation of group spokesman.
It's quite hard to nail down exactly what is happening within Boko Haram right now, but basically, the group is in the middle of a leadership struggle.
On one hand, no one's heard from Shekau in a while - nothing really concrete since last March - so Barnawi, who was already spokesman, became the new leader.
But Shekau, who appears to be alive and kicking after all, said he was still very much in control.
"Rather than the end of an era, this looks like the beginning of a new era," Jacob Zenn, an analyst of African Affairs for The Jamestown Foundation and consultant on countering violent extremism, told RFI.
"Shekau is still claiming his old position. However, while before he was able to control several different factions, this is the first time he's lost a power struggle."
IS trying to assert its power in the region
According to Yan St-Pierre, a counter terrorism adviser who works for a group called Modern Security in Berlin, IS saw this as an opportunity to say 'look, this is our man, this is how it goes, we call the shot'.
There is still a strong component within Boko Haram that is still behind Shekau, and he says 'no, we're still here, we're still vocal, his audio message mentioned clearly Boko Haram by its original name, instead of referring to its IS's name, although he did still call al-Baghdadi the Calif... but it shows that the power struggle is going on, and it appeared a necessity within that internal process to either try to put an end to it or bring it to the next phase."
Nigeria is very important in Africa, so for IS as well, in terms of its economy, its location, its democratic power. It would be smart for IS to declare it has that kind of reach.
"This is propaganda for them, this is, in many ways, them making such an announcement, saying something like this, it's a demnstration of their geographic reach," Elizabeth Donnelly, a Nigeria political analyst with the ThinkTank, Chatham House, told RFI.
"It does not mean that it's true, it does not mean that geographic reach is actually grounded in reality, in practical terms on the ground. Boko Haram, although it has evolved certainly over the years, has very much remained its own organisation, staying within northeast Nigeria, and the region, staying local in that respect."
According to Yan St-Pierre, IS also has to show it is still going strong, because they are losing ground in the Middle East.
"It's a very big foothold in West Africa. IS has problems in Libya, they have problems in their own backyards in the Middle East, in Syria and Irak. Boko Haram is sort of the getaway to West Africa and a lot of problems that are there," St-Pierre said.
"There are a lot of unstable governments, there's a secutiry vaccum in that area, so by using Boko Haram as a door, a possibility to access the west african market, they open doors to more territory, another market, and more resources, in another area where they can try to implement themselves and their ideology."
The first option would see Boko Haram imploding.
"We can expect different factions to emerge. The fact that Shekau has been sidelined, he will want to prove that he is still the most dangerous person out there, or the strongest person to lead Boko Haram, or to lead any group that can continue to terrorise Nigeria," Martin Ewi, a counter terrorism expert with the Institute for Security Studies in South Africa, told RFI.
"He certainly is going to create another group, or join the faction that is pro Al-Qaeda, which has been silent since the allegiance was pledged to the Islamic State armed group. So we can expect Shekau to become even more radicalised."
Such fragmentation could also help the army which has been fighting Boko Haram in the northeast.
St Pierre said this could be a serious advantage for the Nigerian army. "Boko Haram, depending on how it bad it becomes internally, will likely be fighting each other, it could become a very violent leadership struggle, and this is going to play into the hands of the army."
He said this could be a way to weaken the organisation, long enough to make them have to readapt and need many years to become a relevant player again.
And some believe this could mean the beginning of the end of the militant group.
"True Muslims are not joining them, Boko Haram is not getting more recruits, some of their fighters are desillusioned, and they're surrendering. Boko Haram has no place in the true teaching of Islam," Ishaq Akintola, a professor of Islamic studies in Lagos and the director of an organisation called Muslim Rights Concerns, told RFI.
"The attempt to change the leadership shows that even IS discovered Boko Haram was on its way out. Nigerians are not sympathetic, Muslims either. They know the movement is dying in Nigeria." He said Boko Haram will be defeated soon.
However, Zenn said Boko Haram has yet to be eradicated.
"They have too many fighters, the high level leadership is all pretty secure. The pressure will stay on Boko Haram, but it's not about to go down anytime soon. They're still capable of powerful attacks, like last month in Niger. They still have a lot of opportunities, and they could try to expand further."
The other "chilling" concern Martin Ewi pointed out though was the fact that in his message, Barnawi never mentioned Nigeria specifically. Instead he talked about launching campaign s against African states, whereas Shekau has always limited his operations to Nigeria.
Does that mean IS is scaling up?