My opinion is that all casting should be done fairly and everyone should be able to put themselves forward for whatever part they want and be judged accordingly. This isn't necessarily a problem for the casting department but for the wider artistic world.
The problem comes with presuming that the author has written default Cis characters. My published play consists of 4 adult characters. Two of them are married to each other. One is an elder academic, the other is a key worker. Although these characters were imagined by me to be cis characters, there's no reason to suggest that the characters aren't trans - the play doesn't address any trans issues but that's not the point. What we need to do is open up the art from heteronormative to full inclusive.
I wouldn't want the only child character to be a trans character - because the dynamic of the play would infer the child was being studied for being a trans-character - which goes against the interpretation and intent of the play itself.
But 4/5 characters could be trans-characters. I think we're operating on the mistaken assumption that trans-characters must talk about being trans, when in fact they could talk about absolutely anything else that the narrative demands. The more this style of inclusive casting happens (and I think it begins with writers and directors being specifically open to interpretation) the more normalised trans-actors will become in theatre and film. To promote equity rather than equality this relies on trans-actors being given a fair go at securing the role and also being better than the cis-actors who go for it - and for directors and writers to be open minded to interpret the character as trans without prejudice.
The opposite is happening, trans-roles are being written by trans-writers for trans-actors to preach to trans-friendly audiences about trans-issues - at least this is the case in British theatre. This is a total misstep - one which I understand completely - but it's arguing for special treatment and complete inclusion at the same time. Such a position is contradictory and the bubble of support for such agitprop artworks are limited. Everyone within the bubble believes they're great, everyone outside the bubble doesn't see it or doesn't care - and the dialogue moves nowhere.
My argument for trans-actors also extends to writing. You don't need to be trans to write a good play about being trans, you need to be a good writer who did the research. Conversely being trans doesn't make you a good writer either, and if you're not, your work shouldn't be artificially inflated off the back of your identity. This applies to all facets of identity. Nobody should be banned from writing about anything - that's my pure liberal position right there. :o)
Thanks for forwarding the discussion.