I was thinking what fugures in Arthurian lore would have made intriguing characters in the show and I came up with the following ideas:
Sir Dinadan - the most carefree, the most rational and merry knight. He has very practical views concerning courtly love and is universally loved in Camelot.
Sir Dagonet - Arthur's fool. He is a comedic character who is made a knight as a jest, The intriguing thing about Dagonet is that he accepts what he is and doesn't try to be something different.
The Green knight/Bertilak - one of the most cerebral and mysterious characters. You can watch the short animated film "Sir Gawain and the Green knight" on Youtube. The poem is very difficult to read.