Any thoughts - good idea or ramblings of a madman?
Your call. I reckon a singlespeed mtb with slicks makes a great utility bike. Stick a dynamo hub in the front for the ultimate in convenience. For longer distances I'd prefer a drop bar.
Just one point - you might need to think about reducing the cog sizes at both ends to get chainring clearance. A 53t is a pretty big ring to clear those "Fatties Fit Fine" chainstays. I'm running 42:15, which must be in the same ballpark gear-wise.
edit: here's my old Rockhopper which was built along those lines. The gear was 50:18, and chainstay clearance was already a problem with reasonable bottom bracket lengths.
http://images1.fotopic.net/?iid=ymwpzx& ... &nostamp=1
Calmes dans le demi-jour
Que les branches hautes font,
Pénétrons bien notre amour
De ce silence profond.