This may venture into speculation territory, but from what I can see, there don't seem to be many remaining aromatc rings which appear viable in terms of mass-producing a new research-chemical.
Well, there are a few that I can see (to give one idea, the benzoxazole ring looks quite promising for a "next step" from my vantage point). However I have no idea on the chemistry difficulties -- the APBs must have been a bit of a bitch for these underground chemists to begin with because it took about two years (and many bad / dirty / crap batches) to get right.
And any potential tweak, of course, may not work. The APBs were probably the biggest win as far as MDMA clones are concerned in RC history, but many of the tweaked MDMA clones from PiHKAL and other research papers never got popular, as they were relatively weak. Some things that looked like a "win" on research papers ended up being pure shit.
One important thing of course is that many of these clones came from research papers or searchable patents. Despite some being crap, you can get a sort-of idea of which ones "substitute for MDMA", some IC values, some chemistry methods, etc. One thing I do feel is that underground chemists are running out of molecules that they can retrieve from research papers.
So practically -- barring new research papers being found -- the cupboard may be much drier in the future. You will need a brilliant person who can apply rational drug design very well (how MXE was found), elsewise you're just going to get all of this random bullshit like the "Serotoni" stuff.
As far as legality is concerned, I do find it interesting how these days it is quite often "legal" prescription drugs that are taking the heat, with people destroying their lives over things like Oxy far more than some illegal chemicals. A lot of very heady people -- think tanks and more intellectual newspapers and the like -- *do* advocate at the very least decriminalization, with outright legalization even advocated by quite a few. It is pretty clear to anyone with a brain that today's drug policy is a massive failure.
It is more the emotional masses, particularly in certain countries with a strong fundamentalist tradition, that drives today's drug policy. How can you counter that? Only very slowly, by proving that responsible usage is possible and that not everyone who tries X dies or gets addicted for life etc. I think marijuana legalization will help in this matter, as it is the best candidate for an illegal drug that many people use quite responsibly.
