The difference being that Splatoon is an online-focused Nintendo game that will probably have legs whereas Bloodborne is a JRPG that sells the majority of its LT sales in its first week.

You have it the other way around. Online Only games like Splatoon are the ones that sell most of the LT sales in their first week, and then drop off quickly. look at stuff like Titanfall, and Evolve. 

And Souls games have ridiculous legs, infact their opening numbers only account for less than 20% of the LT sales. 

Nintendo's high profile releases are renowned for their legs, especially multiplayer focussed ones like Mario Kart and Smash. Splatoon will very likely continue this trend; I would not be at all surprised if it too sold less than 20% of it's lifetime sales week one.

Are you seriously lumping Splatoon with Smash and Mario Kart?lol

I think it'll be more in line with stuff like Wonderful 101, or at best Pikmin.

In terms of raw numbers? Of course not.

I am suggesting that Splatoon will have the classic Nintendo legs that so many of their franchises have, though.

And you do realize Wonderful 101 is at 330k sold after nearly two years, right? If you want to make a bet that Splatoon will sell around that amount, I'll take it anyday. A month of sig and avatar control?

I don't expect it to sell only 350k, but I'm willing to bet it won't pass 1 million.

How much do you expect it to sell lifetime?

750k-900k. 

I don't know if I'd call that "in line" with W101, which will be lucky to hit 400k.

It's more in line with that than it is with Smash and mario kart...