@ Demi
Well, dunno. Chifuyu doesn't seems to be concerned with tech, and even by theory, an I.S. will grew stronger overtime no matter the base tech. I once talk about it with Age.
In ST, Kurogane is SUPPOSED to replace Kurezakura, but it's one hell of a monster that Chifuyu's successors unable to use it at all and thus the machine fall into obscurity as she retire, that is, until Ichika and Madoka get a touch on it...
As for Tabane ot Ichika, not more than she is for Chifuyu or Houki. At least, Ichika is more important than her own parents...
@ Eras
Poor Aria, feel free to blame your daddy.
(I sense Saya no Uta reference somehow
)