In my opinion this runs counter to the idea of federation; i wouldn’t use it.
You probably do intend to keep it running for ever, but if you can’t for whatever reason, all links created using this service become dead links. If this were client-side, maybe. But this needs a server to be running at lemmyverse.link and/or threadiverse.link. Imagine someone else gets hold of those domains. They can snoop every use.
I have multiple accounts and might want to choose based on what I’m researching. If it were on a client, it should be a widget, but this doesn’t allow me to switch that so easily.
I think the solution should be for all Lemmy clients to detect links when possible and open them up in-app and/or have browser plugins that can redirect requests on the user’s machine. These won’t cover all the cases that your service can, but i would still prefer that over all Lemmy links being resolved by a centralized service that can read your cookies.