Is there a timetable/ plans to release buit-in support for Svelte?
I don’t think so. Maintaining such integration is lots of work - I can tell from experience as the maintainer of the ionic-svelte lib.
Next, getting the integration right is also pretty tricky. If you need pixel perfect copy of the other integrations, then in Svelte(Kit) you may end up creating your own router given the way it handles components and loading.
Maybe when Svelte gets higher in demand (and e.g. SvelteNative does not suffice anymore), there may be more incentive for the company?
Either way, I reckon your message does make a difference 
the juice is not worth the squeeze.