this season is a fire sale with two leaving after this season. just clearing house for the new arrivals next year. of course i am only guessing.
given that the uk shameless lasted 11 years, 20 plus episodes w/over 45 min, i think there is plenty story to tell, it's just in limbo.
i was even thinking several weeks ago, it was odd that the us version had held onto so many characters this long. for example, the uk version ran fine without fionna, as she was only part of the series for the first two seasons.