Cool analysis, let me add some considerations, if you don't mind:
* BMTH will probably be in the book: 2015 was a success; although the experiment of the APE of last year was unsuccessful, so I doubt they will make them headliner.
* Hard to believe that The Killers will be around from june til august, they are too big to be in need to do 3 months of festival circuit. On the other hand, it seems pretty obvious that Sziget this year is aiming for Bon Iver, which apparently share with the Killers the same target, so I'd believe they will focus on Bon Iver rather than obtaining an expensive contract from The Killers.
* Armin is big enough to headline an EDM spot. If Kygo did... Anyway, it would be a co-head name, I doubt it can be able to carry a whole day as Garrix did. An option could also be to have an extremely powerful Party Arena for the day, in order to charme the EDM fans. Dimitri Minchia & Like Pirla could be an answer to that, as they are extremely acclaimed in Hungary. IMO, SHM would be too expensive - otherwise they would have done it this year past.
* MCR are very popular among the teenagers of 10 years ago, so I doubt they will appear. Moreover, being a reunion, I doubt they will have a light cachet and will be down for anything different from an influent spot, so no, I think they are not high in Sziget's priority, sadly.
* Haven't heard a thing from Vampire Weekend so far, so I rule them out for now (anyway, they are classy and Sziget does not look to keen for class lately, but every year they pick one or two names out of the bucket); while Tame Impala are expected to do something: it is all about the period they will decide to play in Europe.
* Nick Cave, IMO, is ruled out by the target and can be considered only as a last resort option, same way The National were this year.
I also want to point out that we may have run out of RHCP, Coldplay, Billie Eilish and Foals, as it looks like they will play in early summer or not play at all. This would put Sziget in a weird position, as it looks like there is a shortage of headliners around (weird, never happens...)