that is right - the work has been rescheduled. I was told that the first stage of formulas will be ready in the beginning of September. However with the current level of work I do not really want to ensure you in any date.
I understand that this may be really frustrating when you only wait for this one thing to be added. I can guarantee that our best developers are working on this project day by day.
How you can track the project:
I think that the best way to track the progress would be by checking updates to the formula-parser repository. It's available at: https://github.com/handsontable/formula-parser
Currently we are making tests and checking how does it work with the undo/redo.
You can also track the profile of budnix - here's a head developer of the formula project.