Actually MOTU is probably the best company as far keeping their old "stuff" usable.
I recently got an 828 MKII (circa 2004) working on El Capitan since they do an amazing job updating drivers/software; that is why other manufacturer's interfaces in the same era go for less that $20 on ebay and MOTU stuff kinda holds some resale value.
There are dozens of other really expensive interfaces that peak out at Mountain Lion or Lower which really sucks for some
Most companies say "sorry, your excellent, really expensive interface, is not worth our time to re-write some drivers... but we have this new _____, oh yeah, it's thunderbolt, so just replace the entire computer, OS, and DAW software while your at it and you can be current, oh, thanks for the call, did I answer all your questions ? survey to follow "