The good thing about bringing back the 17" MBP would be all the objections over battery life and low power GPUs would be moot. Even a thin 17" is going to be huge. The last one looked like 4 cafeteria trays stacked up.

I'm just not sure that there is much of a market for it. It's fun to imagine though. Mobile Xeon, ECC memory, 32 or 64 GB DDR4-2400 RAM, RAID NVMe SSDs. Priced like a Mac Pro :)