Transitions to new language semantics

[mw]

> I would find it much more reassuring if a comprehensive 
> solution was developed as a completely separate compiler 
> branch. Basically have a stable branch (as is), and then a 
> future branch that is considered unstable until all the corner 
> cases have been ironed out.

Separating `stable` release vs `development` experiment branch is 
something that have been discussed on this forum for so many 
times, (last time I remember is `safe` vs `system` by default 
discussion).

I think what we need is action! I.e take it into action. 
Seriously.