Anyone understands if the internal SSD storage can be user upgraded? What connector are they using etc?
The daughter cards hooked to the T2? Probably not. Even if got the connector correct there is a Apple buffer chip that connects the NAND chips to the "line in" from the T2. Apple probably isn't going to sell that and seems doubtful someone will reverse engineer it. (at least any time soon. If it is mainly a simple signal booster perhaps someone will try. ).
It looks to be the same system they used in iMac Pro. Good news / bad news probably means they'll use it again so the replacement parts should be around for a long while.