I don't have a program that uses it, so it's not my place to watch mailing lists for it getting deprecated. Basic searching of Github however (what I'd have expected them to do before removing it) reveals 20k files that contain IPPROTO_UDPLITE, and many projects that use it directly. Probably the most renowned is FFmpeg (!!!).

https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/udp...

https://github.com/search?q=IPPROTO_UDPLITE&type=code

https://github.com/tormol/udplite

https://github.com/nplab/packetdrill

https://github.com/python/cpython/blob/4e96282ee42ab51cf325b...

https://github.com/search?q=repo%3Aviveris%2Frohc%20udplite&...