Doubt it. Not a trivial problem to solve technically and console pricing is inflexible - they need to sell this thing for under $400, and Nintendo hates subsidizing hardware.
Is it? We're not talking about load balancing GPUs - we're talking about a GPU just disappearing underneath you (like when the user picks up the Switch), while maintaining context and dynamically lowering quality - I can't imagine that being a trivial problem.
But that's not the major issue here. Nintendo is going to have to sell this thing for under $400. A mid-market smart-phone costs that much. Shipping a dock with a high performance GPU along with the actual portable isn't going to happen.
This all presupposes, though, that the hardware they're packing in the portable unit is comparable to what's in the PS4/XBO or their newer equivalents.