I think from what was on their survey in the questions about next season we can tell Topps are considering what I believe are the generally good potential ideas. Dont forget that the motms/hcs reflect the awards and standings of players and teams in the previous season. Remember if they add too many card types the collection will get boring, while some cards that have little or no function in the actual game are not necessary. For example the Club badges and legends will only appeal to the collecter more interested in the club's background ect whereas the target audience will have barely any interest. Im going by probability here but even find when collecting the German series that the badges are a bit pointless, If im being completely honest, while I bet you cant find a person who never liked the international legends subset this time around.
If I were to make a guess, I would think they are almost certain to return for the new series, along with either Club Badges or referee cards, because they are on the same level of influence in the game.
(Badges help in sorting for trades ect and are a proper sized subset)
(Referees could be used in a game but for some people may confuse things, and there woulkd only be a few in existence)