I wouldn't even do that.
You don't need mcdaivd to win a cup.
If Mather/nylander become elite winger...you lose that trade bad, really really bad
You need a 1C to win; Matthews will get there, so I'll take the extra top 6 player, all day, everyday.
Let's say McDavid, Matthews, and Marner all reach their potential ...
* McDavid is Crosby
* Matthews is Toews
* Marner is Kane
= 3 Stanley Cups > 2 Stanley Cups.
However, let's be realistic.
* McDavid becoming a Crosby is FAR more realistic than Marner becoming another Kane.
* Furthermore, McDavid is more marketable than both Matthews and Marner. Look what McDavid is doing in Edmonton. Matthews and Marner wouldn't garner the attention if they are not in Toronto. Just from just a bottom line standpoint, it wouldn't make sense.
* Crosby costs the Penguins $10mn+. Toews and Kane costs the Hawks $20mn+. You can see how it matters from a cap perspective.
BOTTOMLINE: Toronto would have to at least offer Matthews, Marner, and Nylander for Edmonton to come to the table. Even then, they'll probably be hesitant. McDavid means more to Edmonton than what Matthews, Marner, and Nylander. Generational talents have the potential to save a sport in a city. Look what Gretzky and Crosby did for Los Angeles and Pittsburgh, respectively. That upside is too much to give up for Edmonton.
So Marner and 2 firsts for McDavid ... or Matthews and Marner for McDavid will not do it. It will take a lot more. I don't know what the first proposal was about. That was beyond ludicrous.