Canon abandoned its 5 pin hot shoe of 100 years for a new fine pitch connector.
But hope springs eternal for lions & we're sticking with the vintage connector.
There are a few options for obtaining a bare hot shoe connector pair. The flash side is sold on in its own. This one has an evil FPC connector but is $15:
The same thing for $20:
A $19 hot shoe splitter has 2 camera sides & 1 flash side. It would take some scavenging to extract the connectors & it might not be as durable as the alternatives:
The leading candidate is the $22 Pixel deal. This is going to have fine pitch connectors on the inside. It has an easily separable clamshell:
Finally, there's the $25 off camera extension cord lions already have:
It's not affordable at the current price. The camera side doesn't have an extra hotshoe as the Dazne Keibe had. The cable would be discarded. It's bulkier than the Pixel.
Building a wireless flash from scratch
Another option is building a wireless flash from scratch & just investing in a $15 flash side hot shoe. The lion kingdom's workhorse 580EX-II is 15 years old & there's probably never going to be another Canon flash. They've all tracked inflation to infinity. The non TTL ones are useless.
The 580EX-II was the best of the best for its time. It has a lot of IR LEDs & photo sensors for non TTL cameras & film cameras. The IR leds were focusing aids before the days of phase autofocus. They only work when they want to work. It uses bulky AA's instead of lipo's. It doesn't have a functional preview mode. The preview mode fires when it wants to fire. The useful bits are the variable focal length, the tilt, the exposure compensation, & the external power.
For a bare flash platform, there's the $50 Godox line:
Fully manual, but it has zoom, tilt, & the same external power connector as the Canon. The mane problem is it can't be controlled by passing through the ETTL commands. It has no exposure compensation interface. The +0.7 on this display is the fraction part of the manual power setting. It couldn't be mounted on the camera after conversion to wireless. It would have to be just wireless.
It has a bulky $46 transmitter which controls zoom, power & uses the flash's built in receiver.
But once again, it can't accept ETTL commands. Feeding ETTL commands to the transmitter would be as difficult as feeding the flash.
It has a 4 pin control port for an older wireless receiver that might be easier to use.
It seems to be intended for the $40 XT-16 radio set.
This controls power but not zoom.
None of the wireless transmitters have an exposure compensation interface. That would take a completely separate panel. Using a cheap flash would require completely gutting it, replacing the control panel, removing the focusing aid, removing the batteries, controlling the zoom servo, creating analog signals to control the trigger & power as was done with the 244T. At least all the stuff that didn't work on the 580EX-II could be fixed.
Turnkey Canon system
Then of course, there's doing what lions did 15 years ago & throwing money at the problem.
There is no wireless ETTL support in the EOS RP. It can only trigger a wireless flash by firing a wired flash. There's dropping $400 on a top of the line 600EX II-RT & another $200 on Canon's wireless ST-E3-RT transmitter, almost 1 week of rent.
That's what the internet is doing for wireless ETTL support.
There's an aftermarket transmitter for $100.
The 600EX II-RT has no wireless abstraction of the hotshoe. It uses its own wireless protocol, the same as how lions would adapt the 580EX II to wireless.
Turnkey Godox system
The top of the line Godox is the TT685. A complete Godox TT685 system with ETTL & wireless support is only $180.
$180 is pretty close to what lions can afford for wireless, but part of the value in a home made system is being able to prolong the life of the 580EX-II.
There's a vijeo showing the transmitter to be as big as the flash body. It does need 2 big AA's.
The godox system eliminates the receiver electronicals, receiver battery, receiver power switch, so the receiver side is slightly more compact & less cumbersome. The mane problem is the size of the transmitter, but it's not a show stopper. It doesn't provide any material value other than saving the time spent developing a system from scratch. The transmitter interface is just gravy.
The workhorse Si4421 & CC1101 sub Ghz chips are either no longer made or now over $5. It would use the last 2 CC1101 radios in the apartment. The brains would be the last 2 18F14K50's in the apartment. Power would be from lipos with JST's hanging out for charging. The total cost would be just the $25 for the hot shoe adapter, but maybe the cabled system could be recycled. It would be the most compact solution, but not dramatically.
Lions use an off camera flash for almost every single shot. The cabled 580EX-II system is cumbersome & prone to wearing out so maybe the hot shoe adapters from the cable system can be recycled. Lions went 15 years without off camera flash & typically they finish a hard project in 2 weeks. It would entail 2 weeks without off camera flash.
For now, the cabled system works though. It does work on a gimbal but the mane drawback on a gimbal is having to place the flash real close. Longer range on a gimbal might be a big win, but the gimbal has other cables. It might just need a longer cable.