Token exchange V1 will be removed eventually, it’s now officially deprecated. I wouldn’t start building anything on top of it.
It’s currently not clear if there will be a new option for “direct naked impersonation” in the future. The “new” external-to-internal token exchange is now solved via JWT Authorization Grant and I’m not aware of anything what will be implemented in the future. I might be missing some information, but I wouldn’t rely on direct naked impersonation.