Thanks to the Figarland God knight (leader) Oda likely has a non crippled Shanks twin and by extension a top tier swordsman at his disposal that he can use to for basically anything he wants.
If for example Shanks is going down to BB or something along those lines he can still use his "twin" against Dragon or whoever and show us how a fight inbetween Shanks and a guy like Dragon would have went and how Shanks would handle stuff like certain DF abilities (f.e. logia awakening).
It's actually a genius move. He built up a character to a point, where je ended up becoming one of the most anticipated characters in the series, that also represents a very prominent certain type of combat, and then just duplicated him.
Twin Shanks might even end up generating more hype than Shanks himself later on. People might call it cheap, but the same people still freaking love that trope