I hope they do something for the 300th episode, something special in the actual show, not the spinoff Hoso.
They might show a catch, maybe even Brock catching a Mudkip!
BTW, we might even see Ho-Oh make a cameo, or even something such as the introduction of Ash's new rival he'll have in the Hoenn Leauge (well, since Gary stopped training, he'll have to have some new rival) or even something as sweet as finally seeing Ash's dad.