Are there real use cases for BGP-LS and PCEP? Are they really useful? Personally I do not think they will ever be used by ISP in their (large) networks.
There are some ISPs that actually care about the network utilization on their expensive long-distance links.
A bit of history
When Cisco rolled out the dismal **** called MPLS-TE in IOS release 12.0(5)T (the manual hop-by-hop stuff that had to be configured on the tunnel head-end router), they told me they already had people who took traffic matrix, fit the traffic to best paths and created hop-by-hop tunnels via CLI. As weird as it sounds, people were doing centralized traffic engineering before controllers became popular and Google started talking about it.
Back to traffic engineering
Anyway, you have to have complex network with expensive links to care. You don't need PCEP as long as bandwidth upgrade is cheaper that continuous network optimization (see also: Terastream), or if you have a monopoly so you don't have to care about customer experience
Then there are the applications that everyone talks about and rarely anyone uses like bandwidth calendaring (reserving the bandwidth for fixed amount of time). The only use case I've heard so far were animation companies or movie studios doing huge file transfer (OK, maybe the CERN scientists would be in the same category, but they probably value money more than time).
As for BGP-LS, every time you care about network topology and run OSPF or IS-IS you could use BGP-LS to extract it. You don't need Northstar controller to do it, people are using BGP-LS with OpenDaylight.
And I do not think that a (large) Data Center needs these techniques.
Absolutely not. DC bandwidth is cheaper than QoS, let alone PCEP.