您不应该使用UniformGrid来替换TabPanel，因为这样会丢失相关的特性，比如正确的多行选项卡项目换行和其他特定于TabControl的项目布局行为。UnformGrid和TabPanel都使用完全不同的算法来排列它们的子节点。UnformGrid没有明确地荣誉TabControl的性质。

方案一

如果您不关心丢失功能或略有不同的布局，那么最简单的解决方案就是将TabPanel替换为UniformGrid。因为您希望垂直堆叠TabItem元素，所以无论如何都会丢失多行特性（默认情况下，多行排列仅适用于水平对齐，即TabStripPlacement设置为Dock.Top或Dock.Bottom）。

<ControlTemplate TargetType="{x:Type TabControl}">
  <Grid x:Name="templateRoot" ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
    <Grid.ColumnDefinitions>
      <ColumnDefinition x:Name="ColumnDefinition0"/>
      <ColumnDefinition x:Name="ColumnDefinition1"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
      <RowDefinition x:Name="RowDefinition0" Height="Auto"/>
      <RowDefinition x:Name="RowDefinition1" Height="*"/>
    </Grid.RowDefinitions>
    
    <UniformGrid x:Name="headerPanel" 
                 Background="Transparent" 
                 Grid.Column="0" 
                 IsItemsHost="true" 
                 Margin="2,2,2,0" 
                 Grid.Row="0" 
                 KeyboardNavigation.TabIndex="1" 
                 Panel.ZIndex="1" />

    <Border x:Name="contentPanel" 
            Background="{TemplateBinding Background}" 
            BorderBrush="{TemplateBinding BorderBrush}" 
            BorderThickness="{TemplateBinding BorderThickness}" 
            Grid.Column="0" 
            KeyboardNavigation.DirectionalNavigation="Contained" 
            Grid.Row="1" 
            KeyboardNavigation.TabIndex="2" 
            KeyboardNavigation.TabNavigation="Local">
      <ContentPresenter x:Name="PART_SelectedContentHost" 
                        ContentSource="SelectedContent" 
                        Margin="{TemplateBinding Padding}" 
                        SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" /> 
    </Border>
  </Grid>
</ControlTemplate>

方案二

一个更简洁的解决方案，尊重TabControl的特殊布局要求，是扩展TabPanel。
在下面的示例中，新类UniformTabPanel扩展了TabPanel并覆盖了垂直排列的布局排列。
对于水平排列，UniformTabPanel面板将回退到TabPanel的默认布局算法。
要使用UniformTabPanel，只需将TabPanel替换为TabControl的ControlTemplate：

UniformTabPanel.cs

public class UniformTabPanel : TabPanel
{
  protected override Size ArrangeOverride(Size arrangeSize)
  {
    Dock itemPlacement = this.TemplatedParent is TabControl tabControl
      ? tabControl.TabStripPlacement
      : Dock.Left;  // Prefer vertical stacking for this panel

    if (itemPlacement is Dock.Left or Dock.Right)
    {
      ArrangeVertical(arrangeSize);
      return arrangeSize;
    }
    else
    {
      // Apply default layout behavior
      return base.ArrangeOverride(arrangeSize);
    }
  }

  private void ArrangeVertical(Size arrangeSize)
  {
    double uniformDesiredChildHeight = GetUniformItemHeight(arrangeSize);
    double childOffsetY = 0d;

    foreach (UIElement child in this.InternalChildren)
    {
      if (child.Visibility != Visibility.Collapsed)
      {
        Size childSize = GetDesiredSizeWithoutMargin(uniformDesiredChildHeight, child);
        child.Arrange(new Rect(0, childOffsetY, arrangeSize.Width, childSize.Height));

        // Calculate the offset for the next child
        childOffsetY += childSize.Height;
      }
    }
  }

  private double GetUniformItemHeight(Size arrangeSize)
  {
    double totalDesiredHeight = this.TemplatedParent is TabControl tabControl
      ? tabControl.DesiredSize.Height
      : arrangeSize.Height;

    return totalDesiredHeight / Math.Max(1, this.InternalChildren.Count);
  }

  private Size GetDesiredSizeWithoutMargin(double desiredChildHeight, UIElement element)
  {
    Thickness margin = (Thickness)element.GetValue(MarginProperty);
    Size desiredSizeWithoutMargin = new Size
    {
      Height = Math.Max(0d, desiredChildHeight - margin.Top - margin.Bottom),
      Width = Math.Max(0d, element.DesiredSize.Width - margin.Left - margin.Right)
    };

    return desiredSizeWithoutMargin;
  }
}

<ControlTemplate TargetType="{x:Type TabControl}">
  <Grid x:Name="templateRoot" ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
    <Grid.ColumnDefinitions>
      <ColumnDefinition x:Name="ColumnDefinition0"/>
      <ColumnDefinition x:Name="ColumnDefinition1"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
      <RowDefinition x:Name="RowDefinition0" Height="Auto"/>
      <RowDefinition x:Name="RowDefinition1" Height="*"/>
    </Grid.RowDefinitions>
    
    <local:UniformTabPanel x:Name="headerPanel" 
                           Background="Transparent" 
                           Grid.Column="0" 
                           IsItemsHost="true" 
                           Margin="2,2,2,0" 
                           Grid.Row="0" 
                           KeyboardNavigation.TabIndex="1" 
                           Panel.ZIndex="1" />

    <Border x:Name="contentPanel" 
            Background="{TemplateBinding Background}" 
            BorderBrush="{TemplateBinding BorderBrush}" 
            BorderThickness="{TemplateBinding BorderThickness}" 
            Grid.Column="0" 
            KeyboardNavigation.DirectionalNavigation="Contained" 
            Grid.Row="1" 
            KeyboardNavigation.TabIndex="2" 
            KeyboardNavigation.TabNavigation="Local">
      <ContentPresenter x:Name="PART_SelectedContentHost" 
                        ContentSource="SelectedContent" 
                        Margin="{TemplateBinding Padding}" 
                        SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" /> 
    </Border>
  </Grid>
</ControlTemplate>