*waits patiently for Devilman,Witchblade or Claymore figures to be made*
Out of those, the only one that's possible would be Devilman.
It looks like Hot Toys is trying really hard to appeal more to the Japanese market and this is definitely their flagship series of figures specifically or that purpose. In other words, they are probably going for the big series that have a good fanbase, most of which would also be willing to pay large sums of money for collector items. In other words, they are likely targetting mature/seinen manga and anime along with things from the 70s, 80, and early 90s, where most of the fans are now adults.
So Go Nagai is definitely very possible. Super robots like the Mazinger would never work because of its odd proportions, which would make doing a good articulated figure difficult and underwhelming. Also, it is directly in competition with companies like Bandai and Aoshima, who tall diecast figures. However, Devilman is perfect. He is a humanoid so the articulation would be no problem especially with how they've handled the Predator figures. He is also one of the single most famous anime/manga figures and my personal favorite of Nagai's works.
Berserk and Vagabond are definite possibilities. Jojo's Bizarre Adventure would have been, if it wasn't for Medicom, but perhaps Fist of the North Star is open to them now since Medicom seems to have abandoned that license.
I do not think most shounen series, even ones like Yu Yu Hakusho, will be bothered with though. The market for shounen merchandising is bizarre. It seems like the more expensive the figure is, regardless of quality, the far less buyers it will have. In general, the market for shounen stuff seems to stray away from figures in general. Companies like Bandai have lost a lot of money due to trying to make use of licenses like One Piece and Dragonball, but getting lukewarm sales.
Hunter x Hunter is possible though, but only for someone like Hisoka or Lucifer. It's definitely an oddball in Shounen Jump's lineup and it has historically been given different treatment in all ways. Char from Gundam is possible. They did him a long time ago and it was nothing special, but certainly possible now. Slam Dunk is a great choice. Kinnikuman would work. Cobra would work, but the problem is that Medicom released a RAH of him and I doubt Hot Toys wants to try to compete with the anime licenses.