I just told my friend about it, and he was sadly bummed out cause he is enjoying a lot using a Modern Sonic mod for Sonic Robo Blast 2, and he wanted to do a full Metroid Vanguard playthrough with one or more friends as Samus players, but he wants to be Modern Sonic more than any other character in Sonic Robo Blast 2. In our second playthrough of Metroid Vanguard he was able to use that Modern Sonic mod, and he was actually kicking lots of ass, he was even capable of using the Boost and Homing Attack to destroy the enemies in DSZ4 without needing Samus to shoot them, and as for the bosses of DSZ4 and ACZ4, he was able to do lots of damage to them, but he required Super Sonic for it, so we got all 7 Emeralds, and he was able to put up a good fight against them. And yeah, this is the second playthrough I mentioned before where we were unable to get Hyper Brak Eggman.
It would be cool that Hyper Brak Eggman only required one player from the co-op party be Samus (100% Powered Up) and have that player's Hyper Beam stolen, and that Samus has to shoot at Eggman's crystals while the non Samus players would use their Super Forms (or even in their normal forms) to destroy the badniks and later do any damage to Eggman when the three floating crystals are shot down and his barrier goes down. It would make a solid game of teamwork where Hyper Brak Eggman is inmune to damage until the Samus players shoot the floating crystals while the non Samus players have to stay alive and distract or destroy the spawned badniks until the Samus player takes down the barrier so everyone can focus their attacks on the vulnerable Hyper Brak Eggman before his barrier goes up again.