I'll be blunt.
All the interviews with Yoshida right now read as damage control in my eyes.
I want to have faith but I can't completely believe that they planned all this to "see how the players would react".

Anyway on topic:
I think the devs are more afraid of leaving the scions behind than the players. Yes there will be voices over them not being in the expansion but I only see two fractions of that tbh.
G'Raha Tia had enough adventures with us for a while now, no matter what his hardcore fangirls think but tbh he is the one I'd have the least problems with (if they keep his crushing on the WoL in check).

The twins are just annoying at this point.
Alphinaud is complete with his character ark and Alisaie is just obnoxious now and only has her sass as a personality trait all centered on us.

Thancred, Urianger, Y'sthola could use a little break and Estinien has no idea what he wants to be now.

Krile is barely a scion and needs far more time to be fleshed out.

Let them take a break (minus Krile) or only have one or two of them with us and give us new characters for an expansion.
The idea of Wuk Lamat was good but horribly used.
The WoL and Krile should have had her, Koana, Bakool JaJa and Zoarl Ja in a team, rotating and interacting with each other.
Later Otis and Sphene would have also joined and done... a good team that had made the betrayal and all the stuff far more meaningful.

Tldr:
Scions need a break,
new characters can work if they actually interact with the WoL (like the scions in the past),
Devs are the ones afraid of leaving the scions behind and not the players.

And yes, I am someone who likes the scions and who has Thancred as one of his favourites.