I somewhat dislike the /proc thing in so far as applications and documentations that assumes _every_ system has a Linuxes /proc structure. But at least Linux didn't invent the /proc idea, just most well known for it.
/opt is defined by the FHS, to me it is largely a waste... But it can have it's uses when desired and /opt is as good a name as any 3-letter combo.
/srv is also in the FHS, a good idea IMHO. My OpenBSD system for example is configured with a /srv/<service>/<service specific files>
for example, /srv/nfs/Videos -> good as place as any to store a big file share that changes so little, it could be RO ;-). Plus it puts in it a fairly obvious place.
/srv for services is no harder to figure out then /usr/share or /var/ either ^_^
Linux "standarts", especially those about dirs or audio subsystem are definitely not the ones that people should go for, its a lot of layers that happen to work instead of one designed facility to do the job done in good manner, the fact that some sh!t is beloved by FHS does not mean that I will take that blindly just because it is aprooved by FHS, same for ISO standarts recently, MICROS~1 did not standarised OOXML, MICROS~1 bought that standart, so if you can buy one no matter how big sh!t it is, the ISO organization becomes useless as a quality determinant.
I also forgot about /sys dir here, we have /proc for all the "kernel stuff" why do we need another one? One big M.E.S.S