Now it sounds like the "end of 2023" will not happen. From WTVJ-TV, NBC-6 in Miami, FL, 12/9/23:
Move over Brightline, Tri-Rail to add expanded services to Miami Central Station
The time is almost here for the Tri-Rail to add expanded service to Miami Central Station. Soon, Brightline will no longer be the only commuter train option to downtown Miami.
Whole story
So there was some concern about whether TriRail trains would fit into MiamiCentral, even though the station was supposedly built with dedicated tracks and a platform for eventual TriRail service. That there was even any question as to whether trains would fit has to evoke thoughts of a nearby situation involving Amtrak moving into the Miami Transportation Center by the Airport.
There also is some concern then about whether MiamiCentral could handle more than one TriRail service-- the rerouted legacy line trains from Mangonia Park, and a potential future line along Brightline tracks up to Jupiter. Plus, with the counties (Broward and Miami-Dade) themselves working on their own commuter rail, where are they going to put those trains?