I think they mean the Tegra daughterboard when they mention the "plug-in card".
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In theory, this could be a very effective and cheap replacement part for anyone with a corrupted emmc, but sadly they will not replace it for you or sell it separately. For now, they will swap the entire mcu at a cost of about €3000.
It is very remarkable that they do not offer to just swap the Tegra pcb, since they used to offer the 3G-4G conversion which is basically the same procedure by removing the mcu and replacing a small plug-in pcb inside. This would reduce the cost of a corrupt emmc repair to like €500-€750 or so.