As to MJB it could be that she is doing other stuff that requires her to not be in so many scenes, either that or that was filmed during the negotations (she maintains work while its worked out), since its been worked out, or when she is done with whatever, they will probably start showing her more and more.
I don't know I don't see them messing up WOAT by bringing on another character, in the last ep i believe her and viv seemed to work well together, getting along imo.
I doubt we will agree on this all i am saying is there will come a time when one character may not get alot of air time, how is it any different then if it were "Sam" or "Martin" or "Danny" getting more time then "Viv" or vice versa?
Alot of people have said, well thats different their part of the "Main cast" well now so is Elena from what we are led to believe. Also while it is insinuated that Elena and danny have a relationship, alot of people are sure its "Romantic" and yeah it might be, but it could be something totally different.
Maybe they knew each other as kids, or the "Baggage" isn't romantic but rather they were friends and had a falling out and or they were friends and something in the past kept them from continuing that friendship.
Personally before i make a decision (and this is just me) whether a character should go, i would like to see where the show is taking the character, why she is there, who she is, and so on, but again thats jmo.