public class Metadata : DynamicObject
{
    ...
}  

...
.DataSource(dataSource =>
{
    dataSource.Ajax()
      .Model(model =>
      {
          model.Id("Id");
      });
})

dataKey = (IDataKey<TModel>)new ModelDynamicDataKey(fieldName, lambdaExpression);

namespace Kendo.Mvc.UI.Fluent
{
	using System.Reflection;
	using Extensions;

	/// <summary>
	/// Defines the fluent interface for configuring the <see cref="DataSource"/> Model definition.
	/// </summary>
	/// <typeparam name="TModel">Type of the model</typeparam>
	public abstract class DataSourceModelDescriptorFactoryBase<TModel> : IHideObjectMembers
        where TModel : class
    {
        protected readonly ModelDescriptor model;

        public DataSourceModelDescriptorFactoryBase(ModelDescriptor model)
        {
            this.model = model;
        }

        /// <summary>
        /// Specify the member used to identify an unique Model instance.
        /// </summary>
        /// <param name="fieldName">The member name.</param>
        protected void Id(string fieldName)
        {
            IDataKey<TModel> dataKey;
            if (typeof(TModel).IsDynamicObject())
            {
                var lambdaExpression = ExpressionBuilder.Expression<TModel, object>(fieldName);
                dataKey = new ModelDynamicDataKey<TModel>(fieldName, lambdaExpression);
            }
            else
            {
                dataKey = GetDataKeyForField(fieldName);
            }

            dataKey.RouteKey = dataKey.Name;

            model.Id = dataKey;
        }

        protected IDataKey<TModel> GetDataKeyForField(string fieldName)
        {
            var lambdaExpression = ExpressionBuilder.Lambda<TModel>(fieldName);
            var fieldType = typeof(ModelDataKey<,>).MakeGenericType(new[] { typeof(TModel), lambdaExpression.Body.Type });

            var constructor = fieldType.GetConstructor(new[] { lambdaExpression.GetType() });

            return (IDataKey<TModel>)constructor.Invoke(new object[] { lambdaExpression });
        }
    }
}

namespace Kendo.Mvc.UI
{
    using System;
    using System.Linq.Expressions;
    using Microsoft.AspNetCore.Mvc.Rendering;

    internal class ModelDynamicDataKey<TModel> : IDataKey<TModel>
        where TModel : class
    {
        public ModelDynamicDataKey(string memberName, Expression<Func<TModel, object>> expression)
        {
            RouteKey = "id";
            Name = memberName;
            Expression = expression;
            Value = expression.Compile();
        }

        public string Name
        {
            get;
        }

        public string RouteKey
        {
            get;
            set;
        }

        public Func<TModel, object> Value
        {
            get;
        }

        public Expression<Func<TModel, object>> Expression
        {
            get;
        }

        public object GetValue(object dataItem)
        {
            try
            {
                return Value((TModel)dataItem);
            }
            catch (Microsoft.CSharp.RuntimeBinder.RuntimeBinderException)
            {
                return null;
            }
        }

        public string HiddenFieldHtml(IHtmlHelper<TModel> htmlHelper)
        {
            return htmlHelper.Hidden(Name, null, new { id = "" }).ToString();
        }
    }
}