Any reason why not?
may slacken off the angles a bit.

it’d be way off. a 26″ fork would be too long.

Cross fork normally ~405 mm long
80 mm 26″ fork 420
100 mm 26″ fork 440
29er fork 470.

What he said.

Run a pace rc31 420mm on an old major jake frame. Works ok. Possibly has a little more flex than a cross fork. Also allows fitting an mtb wheel up front. I did run a 29er wheel for one ride. Was ok handling wise but i did worry about ripping the headtube off.

Any reason why??

There may be better options.

muckin around… I ride cross, was considering doing a few XC raceas and cant pass another bike past SWMBO scrutiny… it was just an idle thought..

Only way would be to try it! My cross bike is a lot lower at the front that my 26″ hardtail. So a fork would certainly radically change the geometry. The cross bike BB is quite low and the head angle pretty steep so it might improve the offroad handling in some respects!