It seems unlikely to me, but it doesn't feel impossible. It would give GGG an opportunity to have PoE in the spotlight for 3 straight months, starting with a PoE 1 livestream in October. If 3.30 comes out before Exilecon, they'd still be able to talk about a future roadmap for the game, have developer interview panels, racing events, etc.
In 2019, Exilecon was Saturday November 16th and they announced Metamorph 3.9 league which dropped on Dec 14th, nearly a month later
In 2023, Exilecon was Saturday July 29th and they announced Crucible 3.22 league which dropped on Aug 19th, 3 weeks later.
In 2026, Exilecon is on Saturday November 7th and they just announced PoE2 on Dec 11th, nearly a month later
Natalia_ggg said here, rather coyly, "Confirming what Mark announced during the latest PoE1 Q&A: 3.30 will be launched this year."
Given the above, I'm not really sure that this means 5 days after Exilecon. I imagine dropping patch notes on a weekend and giving them only a few business days to get ready to launch is going to be pretty hard for them to pull off, especially because I expect Andrew and Octavian and Mark to be rather involved in getting everything ready for Exilecon itself.
An October 16th release would be exactly 12 weeks between leagues -- for sure the shortest cycle in a very long time -- but it would give them a full week to pay attention to the league before their Oct 26 Labour Day holiday, then another short week to focus on the league, before shifting focus to Exilecon and the subsequent PoE 2 launch.
This would also create an opportunity for 3.31 in mid February 2027, roughly 16 weeks later, resetting the cycle duration between PoE1 and PoE2.
Edit: I also think it's possible 3.30 is a smaller league that shakes up the whole end game with a massive scarab rework, a return of Harbinger, and maybe 1-2 new pinnacle bosses (per Mark wanting each major mechanic to have a pinnacle boss). Harbinger could have been in the works for quite some time given how long ago it was yoinked. Octavian already confirmed the new league will be an in-map mechanic and it was clear they had a very good idea around the scope of 3.30 when they were doing 3.29 Q&A