Sorry for my really late reply to this! I would say that RPG wiki banner at the bottom of the homepage is enough and anything additional might make it look unprofessional, but if the logo could be added neatly I would be in favour of it.
>> I would say that RPG wiki banner at the bottom of the homepage is enough
That's my thoughts too.
I'm not sure the logo would be appropriate because it's the logo of the pre-merger Square (that DX has nothing to do with) and not Square Enix. And to be honest, I don't think the idea of "link exchange" is worth it just for the sake of getting an incoming link.
I'd rather just add the wiki link to the Square Enix page.
>> but if the logo could be added neatly I would be in favour of it.
I tried a couple of things... In our current layout, the logo could be placed in the lower right corner, under "Quote":
But on small-width screens where 2-column layout is used this will look a bit less neat - with empty space in the adjacent column. However, this is the far bottom of the page, so the empty space might be not a big deal.