Think yourself lucky it isn't Kings Cross Thamelink still, for a long time fitting out the St P. box was very much in the balance.
If St Pancras hadn't been fitted out, I suspect the whole Thameslink project wouldn't have happened. There's no way the old station could have been prepared for what is planned to one day operate (up to 24tph).
TL and GN would have almost certainly been kept totally separate today.
Incline lift?
I wonder why travelators aren't considered as alternatives to lifts and/or escalators? Obviously they need more room, but you do that at the design stage.