> If there is a way to make something like this accessible to screen readers in some useful way
If by "something like this" you mean a text editor, then there's no question; they can be made accessible with a screen reader, and some complex ones (e.g. Visual Studio Code, Visual Studio, and Xcode) are accessible already.
> it would likely involve specific accessibility work either way.
For the main UI of a full-featured programmer's editor or word processor, that's definitely true.
What I want to avoid is developers using a custom GUI toolkit where the platform's native toolkit would do, because they want the best possible performance (regardless of whether the platform's toolkit is good enough), and forfeiting all of the accessibility benefits that the platform's native toolkit brings more or less automatically.
One of the cliches of modern business is: don't outsource your core competencies.
If you are developing a text editor, you should put the time into your text editor. It's the thing that distinguishes you from your competitors. And it's the part that users interact with the most. Your users are likely to ask for features, like vi keybindings, that you can't easily build with the OS-native text field anyway.
Incidental forms, like your preferences screen? Unless you have a lot of time and money to burn, the OS widgets will probably be better than yours.
If by "something like this" you mean a text editor, then there's no question; they can be made accessible with a screen reader, and some complex ones (e.g. Visual Studio Code, Visual Studio, and Xcode) are accessible already.
> it would likely involve specific accessibility work either way.
For the main UI of a full-featured programmer's editor or word processor, that's definitely true.
What I want to avoid is developers using a custom GUI toolkit where the platform's native toolkit would do, because they want the best possible performance (regardless of whether the platform's toolkit is good enough), and forfeiting all of the accessibility benefits that the platform's native toolkit brings more or less automatically.