User blog comment:B214/Question & Answers 5/@comment-98.227.238.52-20150513171226/@comment-26285797-20150514033408

Since we are talking about the possibility of the Heavenly Dragons fusing together in some way, yes it is possible. But I don't think Vali is able to use Ddraig's power. The only reason Issei can use Albion's powers is because of he fused one of the jewels in Vali's Scale Mail with his Sacred Gear. Besides, it goes against Vali's personality for him to use Ddraig's power. Vali becomes powerful by himself while Issei becomes stronger with the help of others.