YC actually funded a company that does art investments! Arthena, YC W17. Not sure about tax stuff but it's definitely becoming popular as way to make safe investments, given that paintings by well-established (dead) artists don't tend to lose value.
I know in France, there was a "solidarity tax on wealth" which was a yearly tax on assets over 1.3million euros. Artwork was exempt from this. This changed in the end of last year and I think it's just based on real estate now.