Negative points aRe: Tin has a very low melting point - so not easy
to solder to anything - and gold and tin alloyed together form
brittle intermetallic compounds. Even small traces of tin in gold can
make the gold unworkable. In theory you might be able to cast a gold
tin alloy, but not sure why anyone would want to.
Positive point is that gold is very heavy, tin is very light and so
the volume of tin in the alloy could be more than twice the volume of
the gold and you could still mark it 14 Karat. You customer would get
a BIG ring for their money.