Chrom could be likely as a Echo Fighter, but he also could not be in the game because there are three things to keep in mind:Fire Emblem is pretty ripe for echoes, IMO. For better or worse
1. With Chrom that would mean three characters from one FE game (Awakening) (I know it's the game that revived the franchise, but still that a lot from one game).
2. FE Heroes is a recent and very much relevant game with a definite future, mobile game or not. It's also one of Nintendo's most popular mobile games, and just like Awakening, and Fates I highly doubt IS would allow their chance to put characters (and stages) from their mobile game in Smash to slip through their fingers, that's like refusing extra money and advertising.
3. FE Three House will be released too bringing about the scenario as FE Fates did for Smash.
Despite all these factors, Chrom still as a good chance to make it in but only if it's with or after another unique FE character. Despite how Sakurai said there was too much FE rep, if IS urges him to rep their mobile game, or future game, and his team and IS can suggest character(s) with a unique moveset, Sakurai wouldn't be afraid of breaking his own rules it wouldn't be the first time.