I am afraid, the feature is not implemented yet. Generally, we implement the users' demanded features based on its feasibility and priority level. Also, we consider the number of requests posted by different users.
Anyways, could you give us details about your desired feature (Goal Seek...), do you need this feature for Aspose.Cells.GridWeb control or for Aspose.Cells library? We may re-analyze the feature accordingly after investigating it for our Issue tracking system.