Eh, I'd just suggest to not focus on the numbers of characters as much. Sure, Namco may have the fewest of the current 3rd party roster. But when selecting characters, that's never been shown to be a priority. It may be a priority for you and others, but it doesn't seem to be that way for Sakurai.
This doesn't mean that Sakurai can't or won't think, "Y'know, I only have one Namco character. I should add another!", but I think what he'd be looking for at this rate is mainly among the following: fan demand, gaming legacy/impact, uniqueness (not just gameplay, but genre), and...I'm sure there's other criteria but who knows?
That's why I see Resident Evil as a pick with a solid shot. If you remove the context of "4th Capcom character" it's easily the biggest series with size and impact from a Japanese gaming company, and while the horror genre may have an Assist Trophy, it doesn't have a playable character. What better series to incorporate that sort of feel than the biggest of them all? It's a multimedia franchise with movies, manga (I think), and it's on par with Zelda in terms of overall "best selling gaming franchises" sitting at roughly $92 million earned through gaming software alone. It's a big deal.
That, at least, is why I think Resident Evil (not so much Capcom as a company but RE as a series) has a great shot. Sure, I love the series and will shill for it. But it's not as if it's a "nothing" series without my shilling. Capcom may have a lot in Smash already, but it's no as if they're not pulling quality series from them. They're picked for good reason.