It's an exciting idea. But passenger trains passing through the channel tunnel have to comply with safety regulations that are specific to the tunnel. Only the eurostar trains comply - DB does not have any trains that are certified to use the tunnel.

As for the sleeper train idea. We (the British taxpayer) paid for a fleet of sleeping carriages - hugely expensive to comply with the special tunnel fire regulations. Then it was decided that there was no market for this so we flogged them to Canada for tuppence. grrrrrrrrr