Finally got off my ass and fixed the weird alignment issues of the flags being 32x32 by cutting down the height.
Also did the same to all countries that have participated in the past, and might participate in the future, regardless of the likelihood of that happening, so let me take you down memory and fortune telling lane. Let's start with countries that participated in the past:
Ukraine withdrew from the contest this year because of the controversy surrounding the contract they would have wanted the winner of the national selection to sign. After it was announced she would not participate for Ukraine, the second and third placed acts also rejected the offer by the Ukrainian broadcaster. Ukraine has confirmed wanting to return in 2020 though, so I consider them a technically active member.
Andorra has withdrawn after the 2009 contest, citing financial difficulties. In the past 10 years, voices in Andorra, including previous performers representing it, have become louder wanting the country's return to the contest, but the broadcaster can't afford participation - they nearly left the EBU even but they were able to negotiate remaining within the EBU.
Bosnia and Herzegovina has withdrawn after the 2016 contest (though having taken a break for a few years prior to that). They are in debt with the EBU and generally have financial difficulties, even though they very much want to come back to the contest.
Bulgaria has withdrawn after the 2018 contest. The Bulgarian broadcaster has gone through a restructuring, including dismissing the Eurovision delegation, and also mentioned financial difficulties as a potential problem. This is especially sad because Bulgaria has become a force to be reckoned with in recent years.
Luxembourg has been out of the contest since after 1993. Along with Italy, the EBU was trying very hard to have them come back, but Luxembourgois broadcaster RTL has absolutely no interest, already stating the struggle of smaller countries back in the 90s. There has been a petition from Luxemborgois people to have the country return to the contest, but RTL ignored that as well. Currently, there is no indication that Luxembourg will ever come back.
Monaco withdrew after the 2006 contest. They came back for 3 contests after over 20 years, did not qualify in the semi finals, and then cited just how bad the chances for small countries are to qualify as the main reason to withdraw. What makes matters more difficult is that the Monegasque broadcaster TMC got acquired by the French media holding group TF1, which might make a return more complicated.
Morocco withdrew after their single participation in 1980, where they only joined because Israel hadn't. A newer broadcaster expressed interest for the contest, but that has been a few years ago, and we haven't heard anything since.
Slovakia has been withdrawn since after the 2012 contest. They cite financial difficulties as the main factor, and have expressed interest in returning.
Turkey also has been out since after 2012. They are boycotting Eurovision because of the Big 5 system, the jury vote split, and also because of acts such as Conchita Wurst. As long as the conservatives and right wingers are in power in Turkey, it seems exceedingly unlikely for it to return.
Now for countries that almost took part but didn't.
Lebanon almost participated in 2005, even was featured on some promotional material, and a song and performer have been selected (it even is a pretty good song!). The EBU inquired if Lebanon was going to broadcast the Israeli entry, which they said they couldn't guarantee, and shortly after, withdrew. They have not expressed interest since then.
Tunisia was going to participate back in 1977, but withdrew for some reason and has not expressed any interest to debut since then.
And last section, countries that have not participated yet, nor almost, and have expressed interest.
One of the most likely debuts within the next few years, Kazakhstan has taken part in Junior Eurovision last year, expressed interest for the main version, and Jon Ola Sand, the executive supervisor of the contest, has stated that they are going to have a discussion whether Kazakhstan, an Associate EBU member, is going to be allowed to participate - apparently this is a discussion that might involve more than just the Kazakh participation.
Another very likely debut, perhaps as early as 2020, the national broadcaster of Kosovo joining the EBU is going to be discussed during the next few months. If they are accepted, which is likely as the EBU has expressed interest in having them along, Kosovo will be allowed to debut next year, or if not then due to time constraints, then very soon after.
Rumours of Liechtenstein debuting at the contest have been flying around for many years now, but the Liechtensteiner broadcaster is not a member of the EBU yet, and has cited that they have not been able to procure funds from the government to both join the EBU and participate in the contest as a result. Furthermore, the director who was the driving force behind a Liechtensteiner EBU membership and contest entry has passed away recently, making the debut of Liechtenstein even less likely.
Qatar is an EBU Associate member much like Kazakhstan, is quite enthusiastic about the contest, and has expressed strong interest about joining it. They also have explicitly mentioned that they would have no problem showing the Israeli entry, and I imagine that they are not entirely unlikely to debut if Kazakhstan is permitted to.
The regional broadcaster of Catalonia, while not an independent country, has brought up the argument that not being an independent country does not mean they shouldn't be allowed to join the EBU, as they do region-specific broadcasts in Catalan. The EBU said they are going to resolve this issue some time this year. That said, even if non-independent regions are going to be permitted in the EBU, the Spanish national broadcaster RTVE is going to be able to veto a membership of the Catalan broadcaster.
In a similar fashion, the Faroe Islands' regional broadcaster has brought up similar arguments to Catalonia, and also proposed a similar national selection format as the Danish one. I imagine that if regional broadcasters, even if not for independent nations, are allowed, then the Faroes are going to be one of the first new members, and will debut in the contest shortly after.
Greenland has expressed similar sentiments to the Faroes, and is in a similar boat as they are.
Final bit, I'm gonna lump all of these together:
Scotland, Wales and Gibraltar all have expressed interest in sending their own entries to the contest in the past, even though they had been denied on the grounds of the BBC representing them with the UK entry. However, both Wales and Scotland have participated in Eurovision Choir, and Wales also in the Junior Eurovision.
It is unlikely that any of these countries are going to be part of the contest any time soon.
Other countries that are technically eligible to join the contest but very likely aren't going to are the Vatican, Algeria, Libya, Egypt and Jordan.
And also, on a similar note, Australia has been allowed to participate until at least the 2023 contest.