I would find it fresh. But also worry a bit for the boy, as it is very strongly associated with girliness. I would like it much better on a boy for sure. But I would still fret over Mr.
Shannon getting beaten up in the schoolyard.
I'm not sure what I would pair it with. An overtly masculine name might make it look even more soft in comparison.
Shannon John? Hmm, looks awkward. Something unisex...
Shannon Rory? Then he might be taken as a girl sight unseen for sure. Maybe something soft but still definitely boyish.
Shannon Felix,
Shannon Tristram? Hmm, those hit the mark a bit better.
Interesting!