I seriously don't think it matters how much ram is thrown at it no ones gonna buy it when Nvidia have upped the performance and dropped prices and it's still a 290x now if it were a 390x that's cooler and less power hungry it might be a different story
Sapphire had their 8GB cards "limited" edition...
Now that competition starts making 8GB cards they will have to make an "unlimited" exition xD
Also with the 290x still beating the crap out of the 980s in 4K this will be an attempt to keep the 290x the king of 4K for a little more while