Saying it as "The consistency of Martin-L\"{o}f type theory extended with
univalence and higher inductive types could perhaps be shown by inventing an
appropriate normalization procedure, but ..."

The point is that adding "in principle" doesn't seem to address Andrej's remark
that the task is made to sound straightforward.

Also took the opportunity to expand two uses of "HIT".

https://github.com/HoTT/book/commit/820fc0b0364c012fcbbcfaf621463e96b8c9d178#commitcomment-3110010