True but characters such as the Chaotix, Fang, Bean and Bark, and others would have been around. And since the main cast was made off of characters with little to no backstory it wouldn't have been a stretch to include them.
Exactly, and those characters to me design wise fit Satam a lot more than the modern designs like Silver or characters from Sonic Riders for example, I'd much rather see Fang, Bark etc. then sega's characters now.
Honestly including new characters is mandatory for any new Season of a show. Even SatAM Season 2 introduced Dulcy. On top of that, nobody said anything about including EVERY character, just what characters you'd like to see SatAMized. Also just because the character appears doesn't mean they have to be well developed or even important. Take Lupe for example, we barely had any time with her. Or Griff. Or the Rhino and Bear Freedom Fighters in the last episode. Easily you could fill a role of one of those characters with Rouge or Shadow without even saying who they were and it wouldn't take away from the main cast at all. Think of it less as a important role and more as a nod or cameo.
I completely agree that new characters is mandatory but I'd rather it be original characters, your suggestion that some of sega's characters could be minor cameo appearences is fine, that works. You said you couldn't see one person suggesting to include every character, I didn't mean that, I meant collectively between posts almost every modern sega character has had a suggestion of how they could be in the show, or it feels like a significant chunk anway. There have been suggestions for Cream, Amy, The Chaotix, Shadow, Rouge etc. I'd be fine with it if they were just cameos, and I'm not really talking an entire episode deticated to each either.
The problem is the Sonic Fanbase hate Original Characters because they tend to be overpowered. Many Sonic fans don't like SatAM because of the large cast of characters that "didn't appear in the games." A good way to expand the audience would be to include new characters from the SEGAverse.
A good example of this would be Justice League/Justice League Unlimited: Honestly we only watched the episodes that featured Characters we liked. I could careless what happened to Hawk Girl or John Stewart Green Lantern, however if Batman was in it, I'd watch that episode.
Same thing if we wish to expand the SatAM fan base. Only including things that appease the long term SatAM fans won't expand the fan base at all. Actually it'll hinder it as not everyone will agree to the route Sea3on goes.
I agree that maybe a couple of modern sonic characters should be added as main characters to attract viewers and expand the fanbase, but (and I know this isn't what you said) if it ever became bigger than that, like "okay let's really get a load of viewers, let's have shadow, rouge, the chaotix, cream, amy, silver all as main characters", then that would just make me think two things,
1. People who hate the show, some who hate it and never even watched it, would be simply coming on board because it's got "omg all my fav madern sanik characters!" in there, they wouldn't be going to youtube or wherever it's being uploaded for Satam or it's characters and story, they'd just want to see more animated modern sonic characters, as if it was a modern sonic cartoon.
2. No one working on this should have the mindset that one of the biggest things about this project is adding a lot of chartacters/ideas from the official series, purely for the sake of getting those kinds of viewers. it shouldn't be anyone's thought process because that means you're not 100% focused on writing the best story you can for season 3 and it just becomes about the numbers. I'm not suggesting at all that anyone's doing that, but when I see loads of people, each suggesting different characters from Sega's vast list, it get's me worried about what could happen later down the road.
Anyway you said it should stay Satam as possible while including some sega characters as both mains and cameos, I agree with that, there needs to be a good balance of characters. I would love an intelligent/badass Big the Cat to be a main character, or a cameo character that appears more frequently than other cameo characters. 
Btw the sonic fanbase is made up of everyone disliking different eras/mediums of sonic all for different reasons, and while I'm sure new characters being op is a reason a certain group of people may hate the new characters, by far the main reason the majority of fans hate new characters is because their dialogue is horribly written and therefor so are their personalities, wether by being bland/annoying/generic/childish etc. and also because we see how unoriginal some of these designs are. Take Silver for example, third clone of sonic now, has a really annoying voice, whiny, his op psychic powers were actually the one thing people were hoping for to be good to make something about playing him enjoyable, but nope sega screwed that up too.
Cuz Uncle Chuck isn't a recolor Sonic in any way shape or form.
Goddamit, I went through every Satam character in my head and forgot about Chuck, you got me there haha. But I don't know, there was something tasteful about how they did it with Chuck, I'm not sure if I feel the same way about Shadow, maybe that's because Chuck was a good character, and Shadows personality was blatently meant to be the opposite to sonic because recolour. but if he was in this series I would never expect a fanfic answer to him being there like Shadow is Sonic's brother or something, I'm sure they'd come up with a brilliant new story for him and why he's pretty much a sonic clone.
