Occasionally I have made a highly decorated cap-lock rifle, but I try to stay within the bounds of tradition at least loosely.
The fact is that the best art work done on American rifles was done in the period from 1765 to 1810. Those were the days of the flintlock.
Now some very fancy rifles were made in the later years, so there is nothing wrong with making one, but very well done art on cap-locks were just were not as commonly made as fancy flinters. I am making a decorated Bedford caplock rifle now, and it is going to be quite nice, but not as detailed in its decorations as this one was.
Another thing we see in museums today are super fancy rifles that were made as flintlocks that were converted to cap lock in the 1830-1860 period. So again, it's perfectly OK to make such guns. It just that I don't get asked to do it very often