But, would the 500 S&W do anything the .450 Marlin or larger cartridges won't?
As far as I can tell, the only thing that the 500 would do is sell more lever guns to folks that just like the idea.
Lots of us are likely to keep our wallets closed even if the 500 comes out in a lever gun, but if enough folks create a demand, someone will eventually step up and fill the demand at full production level. Guys, if you really want this gun, you're going to have to ask the companies to make it. If they perceive a big enough demand, they'll build anything that won't get them sued (and a few things that will).
Still, if they couldn't even make a .475" round work, and they're not willing to retool for that, maybe you shouldn't hold your breath for Marlin to redesign their models, or add a new one.