I would like to say something like, nous sommes les misérables, but I'm aware that the pronoun nous is rarely used in Francophone countries, or at least in France.
If I wanted to use the pronoun on instead, would it make sense to say on est les misérables? Would this sound natural to a French speaker?
Yes, on est les misérables is perfectly grammatical in spoken French where on has almost completely superseded nous as a subject.
Speaking about les misérables, Victor Hugo, Les Misérables author who isn't especially known to use "improper French", "low French" or for being a football fan (Sorry @CédricVanRompay, I couldn't resist ;-) ) wrote these verses in his Alsace et Lorraine poem 1872, Toute la Lyre:
...
Se ruant sur l'auguste et sombre genre humain.
On est les chefs de l'ombre et l'on a dans la main
Les rênes des chevaux du sépulcre, on excite
...
On gonfle le flot noir des légions sinistres
On est les dieux ayant les démons pour ministres ;
However, in your sentence les misérables looks odd.
Perhaps did you want to say:
on est misérables
on est des miséreux
on est dans la misère
?
In any case, a famous phrase using the on est les pattern is On est les champions.
A written, formal document will likely use nous sommes les ... though.
The use of on in place of nous is considered as informal [1], but in certain structures in just sounds weird, and "On est les [...]" is one of them. "On est les misérables" will not sound "incorrect" but just... "low French".
@jiliagre mentions "On est les champions" which is indeed a thing, but it comes from a very specific context, namely football fans, which is not considered as a reference for proper language. Actually the fact that it "sounds a bit weird" might have help it becomes popular.
However it is interesting to note that "On est + [adjective]" is not considered as improper.
[1] There are other uses of on which are very formal: "On voit clairement que ...", "On retiendra que..."
