Tokens go to ANY zone they are sent to. They cannot leave there, and cease to exist as a state based action.

111.7. A token that’s in a zone other than the battlefield ceases to exist. This is a state-based action; see
rule 704. (Note that if a token changes zones, applicable triggered abilities will trigger before the
token ceases to exist.)

111.8. A token that has left the battlefield can’t move to another zone or come back onto the battlefield.
If such a token would change zones, it remains in its current zone instead. It ceases to exist the next
time state-based actions are checked; see rule 704.

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The transforming token rules change was in March of the Machine, and applies only to transfroming the token. Exiling and retunring transformed is something a token CANNOT do.

Tokens don’t go into exile and cease to exist except if it’s a token of a transforming dfc which they implemented special rules for in ixalan.

They won’t update rules for 3 or 4 meld cards.

That is intentional. Meld requires the pieces to be the actual cards. The meld trigger may recognize a copy as a piece for the trigger condition, but meld itself does not. Even if it did, due to a token being involved, it still wouldn't work, since tokens cannot leave the zone they are sent to. For a melded permanent to enter the battlefield, both pieces have to come out of exile. If either can't, the other stays there, too. If the pieces in exile don't match a meld pair, neither card comes out of exile.