I doubt it.
Itachi is the only person in the world [At the time anyways] who could use Amaterasu, so I don't see a point in improving against a jutsu that Jiraiya would probably never see again.
And plus, the toad stomach jutsu isn't a jutsu that you can like use all the time or is like the staple of Jiraiya's offense, it's a jutsu that needs VERY specific circumstances in order to work.
1. You need to be in a corridor of sorts
2. You need to be in a LONG corridor, because if it's just a little hallway your trying to use it in, the person will escape before the stomach closes.
3. You need to be facing a slow opponent
Not very versatile, if you ask me.
And another thing, why didn't Itachi and Kisame just run out of the stomach before it closed?
Itachi is easily top 3 fastest ninja in Naruto, and Kisame is no slow poke either, so tell me why Itachi and Kisame didn't just run out of it?
I know that's not as fast as they can run, I've seen the anime and it looked like they were jogging inside the stomach....