Five years is a long time!Marans are based on Pti-1L(only!), Id, W
Barnevelder have Id, w+
It is not so complicate to create clean shanks (as proven already by Lord Greenway (the creator of english Marans), in five Years, if You have only to deal with Pti-1L!
There are many clean shanked varieties in breeds, which are based on Barbu d'Uccle, but they managed it aswell, even if they had to deal with the selection against Pti-3 and Vulture Hocks (v)
PS: With Pti-1B (Brahma) would it be more difficult. Pti-1B is dominant over Pti-1L (Langshan).
So You have to deal with 2 genes in contrary to at least 13 egg shell genes, who noone knows how they are really controlled.
In Germany and the Netherlands the show breeder crossed in Wyandottes in Barnevelder and Leghorns in Welsummer and destroyed by this way, the egg shell colour.
This fault can't be recovered probably for many decades.
You still have to deal with the 13 egg shell genes regardless of which breed you choose so that argument doesn't stand up, so perhaps we had better agree to disagree.
I do agree that the rush to produce every variety of every bird regardless of the breed standard is a big problem, the problem is you don't need to show the egg to show the bird or vica versa. And there is a major problem with bad breeders trying to make a profit selling hatching eggs on the likes of ebay!