In this method:

-------------------------
procedure TWidgetImpl<T>.SetInstance(const Inst: T);
var
  ctx: TRttiContext;
  typ: TRttiType;
  m: TRttiMethod;
begin
  typ := ctx.GetType(TypeInfo(T));
  m := typ.GetMethod('Initialize');
  if (Assigned(m)) then
  begin
    m.Invoke(TValue.From<T>(Inst), []);
  end;
end;
--------------
I have a private var (fSubscriber) of T and I get access like this:

typ := ctx.GetType((fSubscriber as TObject).ClassInfo);
....
m.Invoke((fSubscriber as TObject),[]);


Your code is different in these two lines. I think I tried to use TypeInfo and didn't work nicely if I recall correctly. 
Is it wrong what I am doing?

Thanks