Infinite
The bad news was that the progression of his Meridians was tied to his cultivation. The only reason he would be able to reach the Heaven Grade was because he was in the Immortal Ring Realm. In fact, he would only be able to reach the Middle Heaven Grade quickly because of this.
If he wanted to break through this cap, he would have to enter the Path Extinction Realm. And, if he wanted to enter the Sovereign Grade Realms, he would have to break into the Dao Pedestal Realm. Only upon becoming a Sky God would he be able to return to the Ancestral Grade.
But, one had to remember that the true path of the Chaotic Silk Meridians was unlocked by Ryu previously. This meant that his Meridians were no longer of the Ancestral Grade, but were actually of the Origin Grade.
As for how far Ryu would have to go in the Sky God Realm to finally fully unseal his Meridians… He, quite frankly, had no idea. The book didn't have such information for him.