I didn't realize James Middleton was a member of the royal family. Wow
We are talking two different categories here.
Royal gossip vs extended family.
The royals will always have someone to gossip about. Harry may be married but there is Beatrice, and eventually others.
Then there are those who are loosely associated with the royal family. The Spencers got some attention. Any in laws of the BRF get some attention if there is something to write about.
Lady Louise and James Middleton have nothing to do with one another. Media speculation didn't move to James, because there were no royals to talk about. Just like media speculation didn't move to Pippa because there were no royals to talk about. There was Harry and the Yorks, and there is still Beatrice and her dating life.
If James becomes boring the tabs may have to find other royal in laws who are of interest. More likely either the Markles will get some more speculation or Edo and his family background. Then Tallulah will.