That would be cool.. I've got some silkies and showgirls that lay green or even bluish eggs.
That cross should have thrown only cuckoo chicks(if marans was the rooster).. presence of non-black shows the marans were not pure for the cuckoo(rather, for the black color).
Barring is very easy to breed out. If you breed the crosses together or back to a silkie you will get some that don't have barring, use those and barring won't be a concern ever again.
Also, if it was silkie over marans hens it would have been sex linked cross- only the male chicks would have barring.
I too have crossed with marans for broodies.(naked neck, asil and phoenix) . so far seems to have been very good cross for that.