product listing in back-office with tax

Is there any way to display the product listing in the back-office with prices including taxes instead of the current "without tax" listing ?

Yes. You can edit the file listing of the view product of the back end for your backend template via the menu Display->Views and then change the code:
echo $this->currencyHelper->displayPrices(@$row->prices);
to:
echo $this->currencyHelper->displayPrices(@$row->prices,'price_value_with_tax');

Now all prices show 0 and the column is no longer sortable. I made the mod in the "listing" view for products categorie for the backend.

Try like that then:

if(!empty($row->prices)){
foreach($row->prices as $k => $p){
$row->prices[$k]->price_value_with_tax = $this->currencyHelper->getTaxedPrice($p->price_value,hikashop_getZone(),$row->product_tax_id,2);
}
}
echo $this->currencyHelper->displayPrices(@$row->prices,'price_value_with_tax');

Now prices show off ! The column is still not sortable and prices are left align instead of right. However, it's fair for me with this if it's too complicated....

The price column is not sortable. The problem is that a product can have several prices which are stored in the different table in the database. So it's way more complicated to sort the listing by the price and it will give out strange results in some cases.
For the alignment, you can just change the <td> to <td align="right"> before that line of code.

I was almost 100% sure that the column was right align and sortable before making the change....
I can live without the sort. For the align, I should have fix this one by myself....

Thanks again for this very robust support