Perhaps, but I still question the likeliness that the mainstream pot dealer would move to selling pills still distributing from the same source. Pot, cocaine, mdmda, etc are available in bulk from illicit sources. Prescription pills usually come from a legal source at some point and come in smaller quantities. From what I hear opium is more expensive because of the difficulty to transport it in its raw form, and therefore sought after.
Wealthier clients usually have a doctor that will write them the prescriptions for a fee. It's not unfathomable that his dealer also had a line on prescription pills, and he did note that he went dry from time to time but still...
My experiences with this are based in canada so there may be a cultural difference there. But the pot dealing crowd and the pill dealing crowd are far removed from each other unless you are in DTE vancouver, and then it's only physical proximity.
In a more common situation, clients that are of a more permanant wealth would demand higher quality pot, hashish and perhaps opium. "New Money" may dabble in cocaine but if they're not uber rich or don't keep it in check that money won't last long.