Hey Loic,
In case you missed them when I posted before, here are links to those interploid seedlings I mentioned below:

http://maprc.blogspot.com/2012/05/interploid-iris-seedling.html
http://maprc.blogspot.com/2012/05/another-interploid-iris-cross-pink.html
http://maprc.blogspot.com/2012/05/pods-on-interploid-iris-seedlings.html

They're not show-stoppers in themselves, but I'm betting that they've got great breeding potential like you've been seeing.
Take care, Tom

----------------------------------------------------------
I have no problem believing in mixed ploidy matings giving offspring.
I have three such seedlings growing out front currently:
'Pink Champagne' X 'Astra Girl'
'Honky Tonk Blues' X 'Astra Girl'
[both of these bloomed this Spring, and both set some seeds]
'Introspection' X 'Easy Smile'
[hopefully will bloom in 2013]
And I have other seeds that I hope will germinate from similar kinds of matings.