This is an open-source add-on!  It aims to replicate the What-If features found in Excel.

This version includes support for creating Data Tables, which generates model outputs for univariate or bivariate models.

If you have any feedback, please leave a review, or visit the project page at 
https://github.com/sajacy/google-sheets-what-if-analysis 

Usage
==========
After installing the add-on, you should have a menu item: "What-If Analysis" > "Create Data Table".

This will try to create a Data Table from the currently-selected cell range.

For example, to create a 2-dimensional (bivariate) Data Table, you need to select a range where the model output (formula) is the top-left cell, and where the two sets of values are provided along the first row and first column. The add-on will fill in the rest of the cells.

To create a univariate Data Table, select 2 columns, with the model output (formula) in the first row, second-column, and the test values in the first column.

Data Refresh
==========
For performance reasons, Data Tables are not recalculated automatically.

Use the "What-If Analysis" > "Refresh Data Tables" menu item to refresh all data tables.

You can also delete data tables by deleting the associated Named Range (Data > Named Ranges), which will be named in the form of DataTable_RxCy. The deleted cell range will no longer be considered a "Data Table" and you may freely edit / clear the cells as normal.