Local tools/skills/function definitions can already invoke any API.

There's no real benefit to the MCP protocol over a regular API with a published "client" a local LLM can invoke. The only downside is you'd have to pull this client prior.

I am using local "skill" as reference to an executable function, not specifically Claude Skills.

If the LLM/Agent executes tools via code in a sandbox (which is what things are moving towards), all LLM tools can be simply defined as regular functions that have the flexibility to do anything.

I seriously doubt MCP will exist in any form a few years from now