I like to use Ideal as a payment form in Matukio. You've already mentioned you're working on it, so, do you have a deadline or targetdate to have this one finished? And how will your Ideal payment work? With Mollie, Rabo Omnikassa, Ogone (Ingenico Payment Services) or something else.
Just noticed that I already had put in the same question earlier Sorry for that. But Ogone is fine to start with. Another partner could be Chill Creations. They have a few plugins for other Joomla Components. Maybe they can take yours along (is easier for you in building )