What problem does this solve or what need does it fill?

bevy_ecs' internal implementation of the default SystemParams use SystemMeta to initialize their states. Yet, only the is_send() field accessor is public to end-users and all other fields are pub(crate).

/// The metadata of a [`System`].
#[derive(Clone)]
pub struct SystemMeta {
    pub(crate) name: Cow<'static, str>,
    pub(crate) component_access_set: FilteredAccessSet<ComponentId>,
    pub(crate) archetype_component_access: Access<ArchetypeComponentId>,
    // NOTE: this must be kept private. making a SystemMeta non-send is irreversible to prevent
    // SystemParams from overriding each other
    is_send: bool,
    pub(crate) last_change_tick: u32,
}

Given that it's possible to directly implement SystemParam (and SystemParamFetch) for user-defined types in an unsafe impl, these fields should be exposed to advanced users.

What solution would you like?

Add unsafe mutable and safe immutable accessors for component_access_set and archetype_component_access, and immutable accessors for name and last_change_tick.