The upcoming runes system in Svelte 5 looks really nice. I think this will fix most or all of the biggest bugs in Svelte 3 and 4.
I did have some concerns about pages that need to edit complex objects, but it looks like you can write a function to "rune-ify" any object without too much trouble. I made a small project in the Svelte 5 preview REPL to try it out. There are probably some bugs there but that relieved my main concern.
Looking at the compiled code with runes, everything is a lot simpler too. No more need for dirty tracking or passing nested context into components for slots. Slot functions are just closures that directly access the runes in the outer component's state now.
The internal scheduler looks more complex than before, but that's to be expected. Importantly, there are far fewer moving parts and the moving parts aren't being generated by the compiler for every new project, which should both reduce potential for bugs and make it easier to test.