I’m not sure if it would necessarily be interesting, but the main early source for Avalokitasvara was one chapter in the Lotus Sutra (Saddharmapundarika Sutra), called, “Exposition on the Universal Gateway” (Samantamukhaparivarta). The Lotus Sutra is one of the early Mahayana sutras, probably from the 1st or 2nd century CE. In this chapter, Avalokitasvara Bodhisattva is said to manifest in any body required to liberate beings, and the long list of the different types includes female forms. So according to that earliest source, the physical manifestation of the bodhisattva is inherently variable. A little bit like being genderfluid.
Later Avalokitasvara was given some attributes of Isvara (Shiva), and the name Avalokitesvara replaced the earlier name Avalokitasvara, and the bodhisattva appeared in different forms with multiple arms, sometimes with as many as 1000 hands and 1000 eyes. In some ways, maybe one of the main attributes of Avalokitasvara is the ability of the bodhisattva to take many forms, including any gender.
I don’t really have a lot interesting to say about the transformation of male Avalokitesvara imagery in East Asia from male to female, but I will say that sometimes the imagery is still male, with a flat exposed chest, and sometimes a mustache. In this form, the bodhisattva still usually has clothing similar to what is seen in the male bodhisattva art of Gandhara and Central Asia, with the crown image depicting Amitabha Buddha. But the female forms of Avalokitesvara are usually of a woman in a long flowing white dress.
The theme of a bodhisattva changing between male and female is common in some early Mahayana sutras, often some of the miscellaneous short ones. Often it is connected to the idea of the emptiness of dharmas (i.e. dharma-sunyata, a common major theme in early Mahayana sutras). A common type of statement in them is that characteristics of “male” or “female” are unable to be apprehended (i.e. by the mind). There is likely some untapped potential to explore the gender implications in that idea.
The connection to the EBT’s is likely most interesting in terms of the development of EBT ideas about emptiness, and discourses on emptiness, and how those principles were further developed and pushed into being a central theme by early Mahayana groups, and how those in turn were occasionally used to undercut more conservative ideas of gender essentialism.
Female bodhisattvas and laywomen are prominent in some early Mahayana sutras. The reason is likely related to royal patronage of Mahasamghika Mahayanists in the Andhra region of southern India in the first few centuries CE. There were some wealthy women who seem to have given royal patronage to the development and propagation of some early Mahayana sutras. In return for their patronage, they were likely written into the sutras. Based on internal textual evidence in some of these same texts, there were different distribution routes going from southern India up to the north, and the sutras would travel along those routes. Ultimately many of them went along the Silk Road to China, where they then were translated and accepted as part of the Buddhist canon there.
These same groups of Mahayanists also developed the ideas of Tathagatagarbha, commonly called Buddha-nature in Chan/Zen, basically about the universal potentiality for attaining buddhahood. So in some ways they could be viewed as progressive compared to groups that emphasized traditional limitations placed on women, or limitations of being a layperson. They at least focused a bit more on positive potential of each person.