XS to me always seemed as the lamest of lame characters imaginable... kind of been there, done that, oh my, how much this new Legion needed a speedster... yawn...
But I confess that my abysmal hatred for the XS character probably only reflects the feelings I had for the reboot as a whole back in 94. She was the first new character -> she was the enemy
Never got over that, even today.
As for original new members, it's hard to imagine a totally new superpower - I think everything has been here already, unless you invent something totally obscure like... Fruit Boy! And even he is just a fruit analogy to Chlorophyll Kid...