I don't think any GM would dare to do it even if they thought McDavid was not the best player available, would be then end of their career if McDavid lives up to the hype.
I'd agree with that. Last night my Knicks drafted 7'3" (in shoes) Latvian sharpshooter Kristaps Porzingis 4th overall. One reporter noted that every front office had at least one person who thought he's the best talent in the draft. One GM was quoted as saying even if a GM thought that, he wouldn't have the guts to take that risk on a European player who might become the best in the draft at #1 over the established top NCAA guys like Karl Towns-Anthony and Jahlil Okafor. He said if you miss on one of those guys you can survive it because the prevailing wisdom got it wrong, but if you miss on Porzingis you get fired.
Not quite the same situation, but it illustrates how GM's think. Absolutely no GM would pick Eichel over McDavid and it's extremely unlikely, from the perspectives of both the seller and the buyers, that the necessary trade price would ever be met. Of course, no GM out there thinks Eichel is the better prospect, anyhow. I'm sure quite a few think that Eichel
could end up better, but that's totally different from considering him the better prospect.