I believe that he will attend the conference and give a speech, as it's in his best interest to gather more funds and support for his campaign. It's going to be a tough battle against Harris, so he needs all the support he can get.
That being said, the impact of the speech should not be overestimated. Trump is not currently the president, and while he is influential, I don't think his current role allows him to have strong impact on crypto regulations in the US. It is also unclear whether he will become the next president and whether he will follow through with crypto promises if he wins. Finally, I don't believe the rumours about Trump intending to declare BTC a US strategic reserve.
If I'm not mistaken, he still leads Harris by 2-3 points the most, so if there is a tough battle, it will be on the side of Kamala as she need a lot of support. And her turning down the invitation to speak in this conference, but hurt her candidacy for Bitcoin and crypto enthusiast in general.
On the other hand, after the assassination attempt on Trump, he has been on the roll and as we say, he had the momentum already in this election. And him as the center of the conference and him giving what the people wanted to hear from him as a pro crypto advocate, might be the biggest decision for Trump as it might catapulted him with a great lead that Harris can't overcome.