Readonly preopened directories

Are there any plans to support this on the CLI for preopened directories? https://github.com/WebAssembly/wasi-filesystem/pull/91

My use case is adding a "scripting" layer to an application where I need to make some files available to untrusted wasm modules. The modules should not be able to modify these files. Ideally this should be done without relying on the underlying OS permissions. Is there any way to do this on the current version?