In Chapter 1021 we see Momonosuke asks Shinobu a favor, which is revealed to be him asking her to use her Devil Fruit powers to mature his body into that of an adult and therefore, become a bigger dragon.
Shinobu refuses out of concern of how dangerous it is on Onigashima, and on top of that, if she does use her powers on him, he won’t revert back and he will still have the heart and mind of a child. Momonosuke states he doesn’t care about that, saying that if he doesn’t take action now, all of Wano will be destroyed.
Shinobu says “your mind will be still that of a child”. This should put all concerns at rest. This just means that essentially Momonosuke won’t gain any training experience and certainly no Haki skills either. He at max will be able to transform into a large dragon to generate enough clouds to prevent/control fall of Onigashima. Which would make it believable.
Momonosuke will gain elemental powers of Dragon and that would come in handy, he won’t be having any experience of using them still it will be a lot of game changing brute power.
Momonosuke might have to give up several years of his future for the future of Wano. Such heavy decisions could actually end up becoming the key moment in Momonosuke’s character development that this entire saga has been leading up to. It’s not going to be a free boost, it will come at a huge price.
The prospect of 2 Dragons fighting over the skies of Wano is pretty exciting. Since this point is going to be a major character development for Momonosuke I think that something very similar is going to follow suit for Yamato pretty soon since now an adult Momonosuke is closer to becoming Oden than Yamato.