bad choice for me 
In fact, IPv6 addresses are clean from spam reputation point of view. Let me explain: Today, when we rent an ipv4 address, it has been already allocated to somebody else before and it is possible that this somebody was a spammer.
On the other hand, when we buy an IPv6 address, no one had it before. So, sending from a IPv6 address helps not ending in the SPAM folder from gmail since gmail receives emails on IPv6.
I also use directadmin and with directadmin with one IPv4 and one IPv6 on the same server. Exim sends from an IPv6 to gmail and exim sends sends from an IPv4 to hotmail. Ipv6 is never a problem & it should the priority according to RFC 6724
In fact, IPv6 addresses are clean from spam reputation point of view. Let me explain: Today, when we rent an ipv4 address, it has been already allocated to somebody else before and it is possible that this somebody was a spammer.
On the other hand, when we buy an IPv6 address, no one had it before. So, sending from a IPv6 address helps not ending in the SPAM folder from gmail since gmail receives emails on IPv6.
I also use directadmin and with directadmin with one IPv4 and one IPv6 on the same server. Exim sends from an IPv6 to gmail and exim sends sends from an IPv4 to hotmail. Ipv6 is never a problem & it should the priority according to RFC 6724