Indo-European languages that have innovated a nominative-accusative distinction for neuter nouns

Question

One ubiquitous and ancient feature of Indo-European languages is a lack of contrast between the nominative and accusative for neuter nouns.

I'll restrict attention to nouns here and not independent pronouns.

This old question asks why the neuter nominative-accusative merger happened, but I'm interested in a slightly different question: namely, whether any languages have undone this merger through subsequent innovations.

This answer mentions an ergative-like suffix -ants that marks neuter nouns in Anatolian languages.

Innovating an ergative case for neuter nouns, though, is not exactly the same thing as creating/restoring a nominative-accusative contrast in neuter nouns, but it does result in a distinction between two core neuter arguments in transitive clauses, so it counts to some degree.

I'm primarily interested in cases where the neuter has been retained and a way of distinguishing neuter core arguments in transitive clauses has been innovated through the introduction of a new case. Merging, say, datives and accusatives across the board would also count. I would say that removing the neuter gender entirely does not count. A hypothetical Romanian-style merger, where the neuter behaves like the masculine in the singular and the feminine in the plural, that happened to distinguish nominative and accusative would also count as a borderline case.

Answer 1

Russian is such a language. Being a Slavic language, Russian has nouns belong to either animate or inanimate class. The difference is how the Accusative case is formed: the inanimate nouns have Accusative = Nominative, while the animate nouns have Accusative = Genitive. In other words, animate nouns have Accusative different from Nominative. However, it is quite problematic for a noun to be both animate and neuter at the same time, since all the animate nouns are either masculine or feminine. Still, there is a number of animate neuter nouns in Russian, those are some names of biological types, classes, orders, etc., for example ‘mammal’ is млекопитающее, literally “milk-feeding one”, this is a neuter animate noun, although in fact it is a nominalized present participle sg., neut. This word and other biological classification terms like that behave completely like animate nouns — they answer the question ‘who?’, they have all the case forms in singular and plural, adjectives agree with them in the neuter gender, e.g. редкое африканское млекопитающее ‘rare African mammal’. And in the singular, it even has Accusative = Nominative, but in the plural it behaves as animate with Accusative = Genitive:

Sg.: Я вижу это млекопитающее ‘I can see this mammal’ (Acc. = N.)
Pl.: Я вижу этих млекопитающих ‘I can see these mammals’ (Acc. = G.)

This is it. And there are dozens of such words in Russian, they all behave the way I have just described: they are neuter nouns which in plural have their Nominative and Accusative cases different. Other examples are: животное ‘animal’, насекомое ‘insect’, ракообразное ‘crustacean’, перепончатокрылое ‘hymenopteran’, etc., lots of them. These nouns are all declined as adjectives/participles, although they are nouns. But there's one more neuter animate noun which is not used in the biological context, it is существо ‘creature, being’, and this one is a “pure” noun, it is declined as a real neuter noun, but still has Acc. pl. and Nom. pl. different.