Hi,
You overestimate IPv6, the TOR capacity is not going to grow much just because there is v6 support. In fact we've been told for years that v4 addresses are out and pretty much everything is still business as usual. My experience is that most people don't like it and don't want it. Every ISP i work with still offers v4 and v6 optional at best.
Don't get me wrong, v6 support would be nice to have but it's far from being at the top of the list.