How bad is this rusted axle and axle nut?

[Newhart111]

I would try brake cleaner aerosol and an old toothbrush on the OP's wheel. Wire brushes have their place, but always should be cautious when threads are involved. Not sure what is going on with the second picture. Does not look good. Is this a before and after???

Second picture is after cleaning it up. I don’t think I have to worry about scratching up the threads on this one. There are none!

 

[D60]

I would try brake cleaner aerosol and an old toothbrush on the OP's wheel. Wire brushes have their place, but always should be cautious when threads are involved. Not sure what is going on with the second picture. Does not look good. Is this a before and after???

Que? I wire wheel rusty fasteners all the time. Like daily. But not at this level of rust.

Still, if your threads are so far gone that a wire brush is going to hurt them, it's a moot point.

 

[XJRiver]

'Not sure how I will get this off when the time comes.'

After removing caliper and rotor

Use angle grinder with cut-off blade. Remove handle (and maybe the guard) slice into spindle nut horizontally once or twice. Then bash the cut(s) using chisel and club hammer. It's hack but it works. Can't avoid nicking the hub edge so replace that too if you want.

 

[Newhart111]

'Not sure how I will get this off when the time comes.'

After removing caliper and rotor

Use angle grinder with cut-off blade. Remove handle (and maybe the guard) slice into spindle nut horizontally once or twice. Then bash the cut(s) using chisel and club hammer. It's hack but it works. Can't avoid nicking the hub edge so replace that too if you want.

Thanks for the idea.