UIThreadRunnable.syncExec(bot.getDisplay(), new Result<VoidType>() {
  override VoidType run() {
    val window = PlatformUI.getWorkbench().getActiveWorkbenchWindow();
    val page =  window.getActivePage()
    page.showView(MyView.ID, null, IWorkbenchPage.VIEW_ACTIVATE)
    null
  }
})

Thread.sleep(2000)

UIThreadRunnable.syncExec(bot.getDisplay(), new Result<VoidType>() {
  override VoidType run() {
    val eModelService = PlatformUI.getWorkbench().getService(EModelService)
    val ePartService = PlatformUI.getWorkbench().getService(EPartService)

    // Try 1
    val eView = ePartService.findPart(InterpreterView.ID)
    eView.parent // NULL

    // Try 2
    ePartService.parts.filter[ find my view  here  ].first.parent // NULL


    null
  }
})

IViewPart view = workbenchPage.showView(MyView.ID, ...);
part = view.getSite().getService(MPart.class);

public abstract class UIElementImpl extends ... {
  @SuppressWarnings("unchecked")
  public MElementContainer<MUIElement> getParent() {
    if (eContainerFeatureID() != UiPackageImpl.UI_ELEMENT__PARENT) return null;
    return (MElementContainer<MUIElement>)eInternalContainer();
  }
}

and

public class MinimalEObjectImpl extends ... {
  @Override
  public int eContainerFeatureID()
  {
    return eFlags >> 16;
  }
}

    EModelService modelService = PlatformUI.getWorkbench().getService(EModelService.class);
    EPartService  partService  = PlatformUI.getWorkbench().getService(EPartService.class);

    // Show view
    IWorkbenchPage page = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();
    page.showView(MyView.ID, null, IWorkbenchPage.VIEW_ACTIVATE);

    MPart view = partService.findPart(MyView.ID);
    // view.getParent() => null, because 'view' is not a part of the e4 UI-model!
    // It is connected to the Model using MPlaceholder

    // Let's find the placeholder
    MWindow window = (MWindow)(((EObject)eView).eContainer);
    MPlaceholder placeholder = modelService.findPlaceholderFor(window, view);

    MUIElement element = placeholder;
    MPartStack partStack = null;
	while (element != null) {
        // This may not suite your configuration of views/stacks/sashes
	    if (element instanceof MPartStack && ((Object)element.parent) instanceof MPartSashContainer) {
                partStack = (MPartStack)element;
                break;
            }
            element = element.parent;
	    }
    }
    if (partStack == null) { /* handle error */ }

    // Now let's change the width weights
    for (MUIElement element : partStack.getParent().getChildren()) {
        if (element == partStack) {
            element.setContainerData("50"); // Width for my view
        } else {
            element.setContainerData("25"); // Widths for other views & editors
        }
    }

    // Surprisingly I had to redraw tho UI manually
    // There is for sure a better way to do it. Here is my (quick & very dirty):
    partStack.toBeRendered = false
    partStack.toBeRendered = true