Probably the first or sixth option.
Although the debut of SD would be a shock so it’s not impossible.
But I am expecting a really cool colorspread with all the seven deadly sins together since this manga will reach 300 chapters.
Ok I just give it a try and do my best reading NS's unpredictable mind. I think in Chapter 300 Estarossa will finally wake up from his dream and eat his bone. All that had happened were just a dog's dream. And thats the end of NNT.
I love the idea that meliodas and arthur would wake up at the same time and fight to duel in the different kingdoms of the series, meliodas DK + magic and arthur SD + excalibur + magic, would be for me the best fight of the series.
I think Mael and Escanor will exchange a few words, find some middle ground, and thus Mael will allow Escanor to keep the Grace, at least for the time being. We could see a snippet of Escano's past from his point of view, get some insights on Rosa and on how Escanor came to be infatuated with her. Could also get to see Ludocei's skills with flash.
On a second thought, Suzuki's writing I find to be unpredictable at times, so "salvation of Sun" might just mean Mael healing Escanor. The actual focus could be on the fight or meliodas's current condition.
Edit::- I just realised that I didn't quite read the title well, and gave predictions for chapter 297 instead. So then, for chapter 300, we'll likely get some coloured pages, Meliodas will probably wake up from his beauty sleep, or we could get some insights on Escanor's backstory as well which will fall under the revelation option I suppose. Toss up, but I think I'll go with the later.
Maybe Eliz is offered the graces but she turns them down saying it goes against her beliefs and that their must be another way. That's when the Supreme Deity pops out of the earring infuriated at her Daughter for not taking up her birthright and proceeds to possess Eliz, take back her graces, and attempt to kill DK Meliodas.