Well it would be ugly and weak but so are many of the world's wheels when they leave the factory, they still have their place.
Maybe the rims that crack are all heat treated after drilling and hooping etc, so they would be now too brittle for new machining.

Here's another untested wild idea:
Rim starting to crack around a spoke hole: Accept that the spoke tension is going to reduce drastically soon anyway. Drill the ends of the crack to stop it spreading, and replace the spoke with a very skinny one at a tad lower tension. The peak tension under bumpage will be much reduced by the stretch in the skinny spoke, but the rim will still be true as it passes through the brake blocks. Assign wheel to light duties.