Well, there have only been 6 Quarter Scale Hot Toys to date. One of those is still to be released. With photos of a seventh teased at Toy Soul late last year. The last three announced or released have been recent movie Iron Men. Take the fizzler Baby Groot out of it, the rest have all been iconic Terminator, Batman, Star Wars figures.
I would put more chance of Iron Man Mk 46 than anything else being the next quarter scale after the Mk 42. The detail and articulation improvements really suit the Iron Man family, plus it is a proven seller at sixth scale. Or failing that, they may listen to fan cries and revisit one of the older classic movie suits like III, IV, VI or VII..