The main problem we have here is that debit cards are a preferred payment method and each country has it's own system. From my experience and other reports I've seen up to 30% of the customers will use a debit card if that option is given. I don't know how many of them would cancel the sale if debit payment isn't possible.
Unless I'm mistaken only WorldPay offers some of the local debit cards, such as Carte Bleue in France, Bancontact in Belgium and iDeal in The Netherlands. Paymill seems to be the only one to offer ELV in Germany.