Will we ever be able to lock single cells in Numbers?

The only way I'm aware of to 'lock' those cells is to gather them onto a single table, different from the table containing the cells you want to remain editable, then locking the table containing the cells to be 'locked'.

Separating the cells, but keeping them on the same table, is another possibility. In this scenario the entry cells are placed at the left side of the table, the 'don't edit' cells are all on the right side of the table.

If the 'don't edit' cells do not need to be viewed by the user(s), their columns may also be hidden.

If the 'don't edit' cells do need to be viewed by the user(s), those cells could be flagged with a fill colour to carry the 'DON'T EDIT" message.

As for the question in your title line, an answer to that is beyond the scope of this user-to-user community.

Apple participation in these communities is quite limited, and does not include participation by members of the product development teams or by Apple Leadership.

You can send a feature request directly to Apple using the Provide Numbers Feedback menu item in the Numbers menu.

Regards,

Barry

Another way to do this is to place a shape with no border and no fill over the cells you want protected - the shape can then be locked preventing the cells underneath from being clicked. It's a bit inelegant, and the cells can still be accessed by moving the cell selection with the arrow keys - but it's one more way to prevent accidental clicking.