Pre-pitch: remove the implicit initialization of Optional variables

listing the previous attempts:

nov 2017 Pitch: Remove default initialization of optional bindings
jan 2019 Remove implicit initialization of Optionals?
jun 2019 PrePitch: Optional variables should require explicit initialization

the other radical way of solving this inconsistency is to introduce some DefaultValueInitializable (?) protocol. Optionals would confirm to it, so could user types.