I think this is less about Sununu being likely to run and more about Sununu being from New Hampshire and wanting to play a kingmaker-esque role -- which will be difficult given that he's struggled to translate his endorsement into numbers in federal primaries. You could also write an article like this about Kim Reynolds, who's been doing very similar stuff (but is very clearly on Team DeSantis).
I'm not sure why Ramaswamy is considered a serious candidate, but former Cranston Rhode Island mayor Steve Laffey, who is also running, isn't.
One might add Corey Stapleton. I think the answer here is that, on both sides, usually it is polling companies who end up determining whether or not someone counts as a serious candidate, and their decisions are downstream from those of media outlets. (They're also usually downstream of fundraising like a serious candidate). Generally, hyper-wealthy individuals capable of self-funding primary presidential campaigns are taken seriously (Steve Forbes sort of pioneered this kind of thing in the 1990s, but it's gotten more common on both sides; consider Tom Steyer or Andrew Yang for Democrats in 2020), while individuals who have
lost their most recent within-party primary are usually not taken seriously as candidates. (Herman Cain stands out as an interesting exception).
My guess is that, whenever the debates happen, Ramaswamy will
probably be invited (although it isn't certain), while Laffey and Stapleton will certainly not be. (My guess is that the cut-off will probably be 'having won a statewide election as a Republican candidate', which Ramaswamy has never done -- incidentally nor has Pompeo -- but there will probably be an allowance for candidates who have fundraised more than a certain amount, which he can probably hit and other non-statewide winners will probably struggle to hit.)
