At the moment external trickery is required to do remote power-up/down of remote Flex 6k radio and soon the PGXL amp.
A much cleaner and smarter method, not needing any 3rd party external weed would be to implement the wake-on-lan feature (WOL/WWOL). Almost all I.T. kit connected via Ethernet has this capability and every decent server is shipped that way as standard. https://en.wikipedia.org/wiki/Wake-on-LAN
I support hundreds of remote access sites and my life would be hellish and very wasteful without WOL. Not a complicated bit of software, no hardware or cable spaghetti needed....a SMART solution.
Please vote if your setup would benefit from this.
The 6400 $$ question: does the new 6k series support remote on/off.
Interestingly (?) a good smartphone has 32 or more power domains that can be powered up/down as needed.
Try an ecoplug. For under $20 and a free app. You can control several of them. I have one on my 6500 and one on a cabinet fan on a DMR repeater i maintain about 100mi away. You can do simple on/off, set times schedules, etc.