I've suggested this elsewhere in this thread, but the analogue nature of it might be useful to current design teams to get familiar with operationally.

Getting contemporary knowledge of the navigation, hydraulic, avionics and other systems is going to be pretty powerful if you need to build something that is as battlefield-ready in the modern era. Nobody is hacking into an SR-71, and it's going to be delivering its missions just fine if GPS is knocked out. Taking the operational (and not just academic) experience of doing that and putting it into the current generation of Skunk Works engineers is going to be useful.

I'm not sure their plan is to put it into active service, but they could - the SR-72 could just be an SR-71 with upgraded engines and other systems.

However, the process of getting it ready for active service even if just as a flying museum piece could sure help a lot of engineers learn a ton of lost knowledge.