My experience in post production in the US has been that people requested AIFF files back in the day (i.e. early 2000’s), then stopped doing that. Now the only request, if I even get one, is for WAV files (or “Broadcast Waves”).
I have never had a request for any other file format. I’d even guess that 95-99% of my customers and their customers are completely unaware of FLAC.
And any other time I’ve been asked to deliver anything other than AIFF or WAV it’s been Pro Tools sessions, DA88 (doesn’t happen any longer), Beta or DigiBeta (doesn’t happen much any longer really) or new HD optical drives.
I’m all for options, but my industry in my geographic location doesn’t seem to care about FLAC.