Possible Silver/Echidna/Ancient connections
In Sonic Chronicles The Dark Brotherhood there is another tribe of echidnas called the Nocturnus Clan. The Nocturnus Clan was incredibly technologically advanced and nearly conquered the world thousands of years ago before they were trapped in another dimension with powerful alien races by an entity called the Argus.
This game and the stuff in it is considered non-canon now due to legal issues that we are definitely not here to talk about but it was canon when it came out and different echidna tribes are referenced in Sonic Frontiers. The ancient portal technology in that game is also similar to the gear themed technology used by the Nocturnus Clan. So there's hope of Nocturnus or a rewritten version of them still being canon. Silver has many similarities to the Nocturnus clan and their creations.
Silver is visually similar to Imperator Ix, the leader of the Nocturnus Clan (Especially the cuffs which are similar to Silver's)
The patterns on Silver's gloves and cuffs are also similar to the ones in Nocturne and the Cyberspace Portals in Sonic Frontiers.
The convex patterns on Silver's cuffs can be found throughout Nocturne.
Silver's front quills have a similar structure to the head crests of the Gizoids created by the Nocturnus Clan.
The big quills on the back of Silver's head are similar to the tentacles that Chaos and The Ancients have on the back of their heads.
Silver's big quills seem to have blood vessels? He puts bandages on them in Sonic Channel artwork and gets blood stains on them in IDW. Maybe they are tentacles?
Sonic Team has foreshadowed connections with visual similarities before. In Shadow The Hedgehog before you find out that Shadow is part Black Arms you can see throughout the game that the Black Arms have red patterns like Shadow and in Sonic Unleashed before you find out that the Werehog is a portion of Dark Gaia you can see that Dark Gaia monsters have the same stretchy arms and attack patterns as the Werehog.
One of the alien races trapped in Twilight Cage with the Nocturnus Clan in Sonic Chronicles called the Voxai has psychic powers like Silver. They have the psychic ability to fly like Silver and control minds.
One of the leaders of the Voxai named Leucosia has the same colors as Silver's powers and patterns similar to Silver's PK Marks.
The only named place in Silver's (good) future that we've seen is Onyx Island in Sonic Rivals. Onyx Island is actually the future version of Angel Island which is the home of the Knuckles Clan, The Master Emerald and Sky Sanctuary. Sky Sanctuary also has advanced ancient technology and patterns similar to the ones on Silver's gear.
We don't know how connected to Onyx Island Silver is but it is the first place we see him after the reset in 06.
This could just be because of his powers but Silver is very upper body oriented. He never kicks like Sonic and Shadow do. Whenever Silver does get physical he always punches things which makes his fighting style more similar to Knuckles and the echidnas than his fellow hedgehogs.
Cyber Sonic's eyes are similar to the eyes Silver has in concept art.
