Actually, I think as cels become more scarce, cel 
painting as a hobby will probably increase in 
popularity among collectors that really want a 
cel from *that* scene.  Oh wait, it already has.  

I agree that painting cels is a mechanical 
process--it's like a paint by number if you're 
not doing anything beyond reproducing a 
screencap.  You don't need any skill, just a 
steady hand.  I'll teach anyone willing to learn; 
for example, I taught my old roommate how to 
paint cels by printing out pictures from old Care 
Bears coloring books.  She couldn't draw for 
crap, but she loved painting because it's really 
relaxing, and the end result is very pretty and 
cool.

But fancels don't have the production value, just 
the 'that looks nice on my wall' value, so a) 
they won't ever become that popular as an 
industry and b) they won't ever become that 
expensive.

So, to wrap it up, I think cels will always be 
around in one form or another.  old production, 
reproduction, fancels, whatever.  they're all 
just paintings on plastic, if you disregard where 
they come from.  But I think the focus 
of 'collectable' production art will switch to 
sketches.