For whatever my opinion is worth, the next logical step would be something along the lines of a Boxed Set to follow on to The Game of Armored Combat set, as a "next step". I think such a set would be the ideal to do the rest of the "classics" or "nuseen" or whatever we are calling them now that aren't in the first two boxes, plus a Star of the iconic Clan mechs and vehicle counters, to introduce all of those rules as the next stage beyond the current Boxed Sets.
It would obviously have to be a somewhat high-price-point set with all of those, but I think it would make a great next step. Plus, just as the Game of Armored Combat set pairs well with the Battletech Manual, this type of an "advanced" set would pair very well with Total Warfare.