Cripping-up and blackface/yellowface (& all associated variations) are just grim. The director of “Wonder” did try to cast a child with facial differences, but after struggling to do so ended up casting Jacob Tremblay, using prosthetics - & then talking up the need to cast more disabled people 
There was a lot published about why it mattered, but I think Ariel Henley’s article for Teen Vogue is particularly clear. (Incidentally, her autobiography A Face For Picasso was published last year.) Last year Sia apologised for her handling of autism in her film “Music”, including the casting of the chief protagonist. There are disabilities that would preclude [some] individuals with them from acting - but with those where there is a spectrum or degrees of severity, having people with the disability draw on their lived experience is preferable to an abled person fully cripping-up to play the role. Things are getting better in contemporary productions when it comes to casting non-white people in roles that don’t specify an ethnicity. Casting disabled people in roles that don’t specify disability, however, is still slightly rarer than finding hens’ teeth by the light of a blue moon.
Both cripping-up & blacking-up are, effectively, a form of punching down. Punching down via artistic expression; not necessarily with malicious intent (the Final Bow For Yellowface project gives a perfect example of yellowface that’s not intended to be cruel); & in the case of cripping-up part of a much bigger picture of using disabled people as props, toxic positivity, tokenism & inspiration porn.
This particular casting is punching down at women - as a PP noted, there is already a marked disparity between [types of] roles available to men & women of Izzard’s age (or simply aged 40+). This is not a bold new departure, even asking the audience to pander to Izzard is simply more of the same egotistical nonsense we see from male actors/producers/directors of a certain age. Film & TV usually expect us to believe that gorgeous [successful] 20-something women are desperately in love with middle-aged men. Now our suspension of disbelief is expected to stretch instead to indulge actors’ personal beliefs about “gender identity” & thus which sex roles they should play - are entitled to play, entitled being absolutely the operative word.
“We could tell you a fascinating, compelling & powerful story with any number of fantastic actresses in the eponymous role… instead we opted to indulge a man’s ego.”
Oh, to have the confidence of a mediocre white man* - may we all be granted it (& ideally paid accordingly, too)
- I used to think Izzard was a very talented comedian & admired the way he learned French to a sufficient standard to do gigs in the language. Now, though, his behaviour is so off-putting I can’t enjoy his work at all. So not, in fairness, mediocre - but he doesn’t seem to have any comprehension of his male privilege at all; let alone the fact it doesn’t suddenly evaporate when he decides he’s “in girl mode”.
(NB: Use of male pronouns & referring to Izzard as male is because Izzard uses both male & female pronouns & has explicitly & repeatedly stated he’s happy for both/either to be used in reference to/discussion of him.)