Hopefully they recognise their niche and stick to it. I'm particularly interested in Svelte for compiling down to vanilla WebComponents to be used in P2P apps (eg Holochain) where you want the end users to be able to modify components themselves.
Here are the docs from v2 https://v2.svelte.dev/guide#custom-elements
So far I see 2 sentences related to the subject, compare that to V2 docs.
I will try to see how svelte performs for this, but so far Vue wc-wrapper seems to be the most promising option out of "non-wc first" ecosystems.