Sparkyx, the guy behind the PI theory, claims erection quality (
EQ) is the most important indication that you're doing things right. Basically, if you train right you'll get better EQ and then you'll gain, in theory. This fits in with your smooth muscle (
SM) theory. You train right and make the SM grow, which means better EQ just as Sparkyx predicts. Since improved EQ comes before gains (PI theory) it may very well mean that you increase the SM first and then the SM stretches the tunica kind of like roots slowly breaking through concrete/tarmac (
1). I didn't see the connection between Sparkyx's PI theory and your SM theory before.
About the megalophallus issue.
"
Megalophallus probably resulted from permanent loss of elasticity of the tunica albuginea due to severe engorgement during the episode of priapism." (
Link)
That is an assumption, but still. This supports the elasticity theory which I believe is fully compatible with your SM theory.