I alway get ABI and API confused. So you're saying, adding a return value would break the BINARY compatibility right so things won't link anymore, right? Because it seems like functionally, turning a void into an int (that people will ignore by default) seems doable.
Also, do we have any plans to allow for breaks ABI in A5? Because if so, I'd definitely put this one on the TODO list when that happens. It seems like an oversight in its current form, and a super simple fix.
For a practical matter for Kev, you could "fork" the function and just call it al_draw_multiline_text2() or al_draw_multiline_text_ex() in your code.
I honestly never realized we had a multi-line text function in A5 (since IIRC A4 never had it) and I always just write my own as it's pretty simple to do a function that works in 90% of cases. (e.g. No auto-wrapping.)