I'll tell you this. I have used H big time before and can honestly tell you that any of the "smacky" rolls you have heard about compare NOTHING to real smack. I don't know why they are called smacky... I just hear that term come from people who never touched smack to begin with... I think it is more a term to describe how the E is rather than a real reference to having "smack" in the pill. Just like saying you feel "cracked out" doesn't imply you just smoked any crack first.
Also, it is very true about these things concerning heroin: a typical dose in the southeast USA costs $30 which is for 100mg, usually cut with something, maybe 70 percent pure at best. But still, this is what is typical in my region. This is a good dose for one person. Take 100mg of street heroin that costs $30 to dose someone (IV use -- heroin is NOT active orally!!) and it makes NO sense to put this in a pill. Less than this would not be a dose that you could feel, even if shot up. And counting in that you can't feel heroin by eating it, and it makes using H as a pill filler even more of a joke.
Even if you were a dealer who got smack at low dealer bulk cost, the price of using it in a pill would be too high to justify using it at all! The better filler would be DXM, which as a powder is 1) able to be felt 2) is cheap.
I have read once in history that there was a pill turned into Dancesafe.org that had heroin in it. The pill was poorly pressed and also had fluoxetine (PROZAC!) and asperin in it. This makes you wonder. Why would a pill be pressed to have heroin prozac and asperin in it? What an odd combination! It makes you wonder if it was a joke? Sent in to Dancesafe.org just for fun? So strange!
But that is the only time I ever heard any credibility to this myth. The better thing to do if you were going to pack an opiate into a pill would be to crush up other opiate pills, like oxycontin or percodans or something. But with oxycontins (pure oxycodone with filler) being usually 50 Cents per mg (10mg for $5), it makes it ludicrous to use as a filler either, even though it would be felt orally and might be easier used in pill form (moreso than heroin, yikes)! The cost to justify this is just what answers your question.
Only an idiot would waste money using any opiate to press with any ecstasy tab. If you want to get the opiate warm buzz, the cheapest way to go would to buy hydrocodone pills at $1 pill for vicodin or lortabs, and eat upwards of 5 or 10 depending on your tolerance (mine is super high). Anything more than 10 would be impossible since the tylenol in the pills would make you sick!!! Very sick! But hydros are the cheapest opiate pill out there (okay, codeine is, but a complete waste of time imho) but always have tylenol in them. So this is off on a tangent, but just the only way I can think of to get any sort of true opiate buzz with a tab of E... to take them separately. Combining them into only pill would be impossible because it would have too low quantities of either in it to be worth the effort.
Seriously. Smack does not feel like a smacky pill in any way. "Smacky" as a term when describing ecstasy has nothing to do with heroin -- it's just an adjective like "cracked out."