1. multirow header columns available?
This feature will possible in the next major version, where you can use column bands to create custom layout of cells.
2. i need to display a image-text-dropdown combination cell that behave as follows : if user click the image, a tree dropdown showup displaying products, if user click the dropdown (multi-column) displaying product code, description, etc. The selected item should display on the text part. User should also be able to enter product code by just typing directly. It should be a autocomplete and in-sync with the dropdown.
Yes it is possible, autocomplete feature will available in the nearest FlyGrid update (end of this week-beginning next week).
How simple is the code to implement item 2 above if not existing feature?
Yes, it is easy to implement, you can see the CustomDropdownColumn example in the Grid Stylizing, Multicolumnar dropdowns, Inplce Editors sample. If you'll need additional samples - let us know.