Why can't we derive struct's?

[Manu]

I've long since become bored of this design decision. Is there good
reason for it?
Why should it be impossible to derive a struct?

It can just be a sugar for an `alias this`, but for a case of simple
inheritance, `alias this` can be tedious to spot and understand when
reading the code.
There's also the special case of an empty base-struct. I
**constantly** have to do this:

struct Derived
{
  static if (Base.tupleof.length == 0)
    ref inout(Base) base() inout { return *cast(inout(Base)*)&this; }
  else
    Base base;
  alias base this;

  // the things...
}

If not that, then the derived class gets an aligned field of nothing
populated by one byte of empty base struct.

It also wastes the single `alias this` slot that we get in a
no-multiple-alias-this world.

As far as I can tell, the decision is arbitrary... can we move past this?