High school 'something' (either romance, shonen, horror) will never go away, it's a staple; but we might get more battle shonen centered around schools, isekai are just battle shonen with a fantasy coating. Fantasy anime may get the short end of the stick because of the close association with isekai and the inevitable comparisons with Frieren, so the genre may be left alone for a while - unfortunately.
I'm betting on a wave of mecha anime driven by Gundam's 50 year anniversary in 2029. Bandai/Sunrise is already warming up with teasers, commemorative videos and partnerships (the Hololive Gundams as an example). You can bet authors will pivot to that genre, chasing the popularity. We might get our scifi, post-apoc and silly space operas because of that!
And maybe a ressurgence of mahou shoujo: there's a lot of anime about witches for a while now, adapting the theme is pretty easy. It doesn't even need to pull a Madoka, a slightly edgy/more mature mahou shoujo from the get go would do the job pretty well. Uma Musume already has proven how grown-ass men will watch cute girls doing silly things if there are high stakes and fierce competition.