Let me take this opportunity to provide a bit of insight about how I look at brand new proposals when they first show up in the proposal listings.
I am not here to pass judgement on every new site idea regarding whether I feel they would make a good site or not. That is not my job. But I am here as an advocate for the process, and we don't generally let folks waste their time on ideas that are not good fit for the network overall.
But when I do close a proposal on day one, it is typically for one of two reasons: either the idea is something outside the purpose for which Stack Exchange was created, or the subject is already being well served by a site on our network (plus a handful of outlier reason not worth going into here).
But if I simply don't know or there could potentially be more behind this idea than I am aware, time is on my side — proposals are not sites — and there's plenty of time to let the process to play out. There is a lot to be learned by the process itself.
Honestly, when I saw a proposal for 'Mint', my first impression was that it would most likely be close as a duplicate of Linux & Unix. But there are only about 1500 of 80,000 questions tagged [mint] on that site, so maybe there's an untapped audience that hasn't been reached by the Linux site; that is, maybe there's an entire axis of questions specific to Mint that would be entirely inappropriate for Linux SE. Or maybe the author is the next Steve Jobs or Bill Gates of Mint and they are about to unleash 642,000+ users unto a site of their own (I call that the "act of god" scenario).
Who knows; a few days of monitoring the 'followers' and example questions can bore that out. That is why I don't always close apparently ill-fitting proposals on day one. But an argument of "our subject is really awesome and huge and will be better served on a site of its own" is typically not a good argument to split off a site. These so-called "exceptional reasons" have to show up in the proposal itself… and they have to happen early on, or the proposal will likely be closed for the reasons I stated above. The definition and performance of the proposal is all we have to go on, and we cannot make assumptions that will make up for any short-commings in the proposal or audience later.