I have been doing this for a few years with my team. I have cross-trained my team in forensics and incident response, and I assign junior staff to work with senior staff. I think it is very necessary to do nowadays with the low numbers of security professionals available. I also feel that growing staff this way helps with team building, career growth, and overall value of the job for retaining highly skilled staff.
Yep, many years of experience, then a weeks boot camp and final day exam. The experience means the questions can be answered from experience, the boot camp is there to remind, and fill in gaps if your experience doesn’t cover all the bases. And also for community and support!