I think you will be quite interested by how Rust handle that.
They have "feature gates" that are annotations (in the source) to enable 
specific features. They also have a notion of stability integrated into 
their documentation.

Le 08/10/2014 18:45, Yotam Barnoy a écrit :
> No, I'm not suggesting turning features on or off as in haskell. This 
> requires no actual programmatic changes to the code. It's just a 
> conceptual labeling of features, indicating their level of stability. 
> It means that when introducing new features, certain parts of the 
> language must be seen as static (or close to static) while others are 
> more malleable or even very malleable.
>
> The ocaml devs can introduce features more liberally, without worrying 
> about future implications as much. If an alpha feature doesn't survive 
> alpha, it'll be cut/modified eventually. They can rely on user 
> feedback to gauge whether a feature is really worth solidifying into 
> the core language. Perhaps there could even be another level: 
> experimental features, which aren't even guaranteed to play nice with 
> alpha or other experimental features, but allow experimenting with 
> ideas in the wild.
>
> It also sets the expectations of the users: if you want to make sure 
> your code will compile in 5 years' time, use only stable features. If 
> you're ok with features that have been around for a while but may 
> change a little, use beta features. If you're not afraid to mess with 
> the latest stuff, you can use alpha level features.
>
>
>
> On Wed, Oct 8, 2014 at 12:35 PM, Milan Stanojević <milanst@gmail.com 
> <mailto:milanst@gmail.com>> wrote:
>
>     I'm not sure that current compiler architecture can easily support
>     your suggestion.
>     It does sound nice but I'm afraid it would lead to a combinatorial
>     explosion in the code, handling different cases where an extension
>     might be on or off.
>     A lot of recent ocaml language extension have subtle interactions with
>     each other that can easily lead to bugs, even unsoundness.
>
>
>     > While I'm not suggesting playing it fast and loose like haskell,
>     perhaps it
>     > makes sense to have stages of integration into the language. I
>     suggest 3
>     > stages, borrowing the terminology from software release cycles (but
>     > perfectly willing to use other terminology or number of stages).
>     An alpha
>     > feature is one that was just introduced, and is still likely to
>     change in
>     > future versions. An alpha feature that has survived enough ocaml
>     version
>     > iterations and seems useful and complete can move into beta
>     level. I foresee
>     > features spending a long time in the beta state, which also
>     guarantees the
>     > users a further level of stability over alpha features.
>
>     So features then turned on and off by level? E.g. all alpha features
>     or on or none?
>
>