The Nintendo Switch uses the Tegra X1 which fits in a traditional power profile of ~10W, but it is somewhat downclocked (about 1/2 the OOTB specs) to drive that

The Nintendo Switch uses the Tegra X1 which fits in a traditional power profile of ~10W, but it is somewhat downclocked (about 1/2 the OOTB specs) to drive that power usage down more, helping achieve its current battery life. So a 10W part can absolutely work, if you scale down the clocks a little bit. The Switch uses a 4310 mAh battery, for reference. In contrast, the TX2 in "MaxQ" mode (energy efficiency savings mode) achieves close to equivalent performance on many benchmarks to the TX1 at half the power budget, so it has 2x the energy efficiency overall. The real question is where Xavier lands on the power/efficiency curve here, but I'm betting it would be pretty good, and there's nothing to necessarily disqualify a downclocked part, here. I think a custom version of Xavier could make a good gaming part, if it wasn't for the cost being outrageous.