It's interesting that this is their first nomination given that they've been a musician for many years
What is your point? If you are trying to suggest this is some sort of "career move" for an otherwise undeserving artist you are miles off.
As Antony Hegarty she was nominated for and won the Mercury prize in 2005 for her second album I am a Bird Now. Under the Antony and the Johnsons name she released 4 studio albums and several live albums, at least 2 recorded with full orchestras. These may not have been huge sellers but they sold well enough and are hugely critically acclaimed. He /she has no difficulty selling out concert halls. Her work uses elements of performance art and the support acts when I saw her were contemporary dance artists, not bands. She is not really run of the mill Brits' award material.
The album which won the Mercury prize has a theme of exploring gender/ transgender issues. The CD cover is that famous photograph of Candy Darling on her death bed; the inner notes have copies of 2 letters dated 1966 by children taken from a medical journal on hermaphrodism and sex reassignment. She is definitely not just band wagon jumping.
The live album Cut the World; features a track called "Future Feminism", which consists of a speech in which Anohni (and I'm quoting) "disparages patriarchal religions and advocates for a shift towards feminine systems of governance as part of an effort to avert global ecological disaster"
I honestly don't know what you will make of this but give it a listen.