If your interest is just in experimenting with different LED’s, coin cell lights like the Photon Freedom or Inova Microlight are very easy to swap 5mm LED’s in and out of.
Speaking of 5mm LED’s and higher end hosts, there’s a product that I think is still available called an “onion ring” that has three sockets for plugging in 5mm LED’s, as well as a potentiometer to adjust output. It is designed to fit in the Surefire A2.
I asked Sofirn: This is indeed the C01*S* driver/LED PCB.
put me down for 2 more, please
That makes interest in 100 hosts now. I’m afraid that Sofirn is still not impressed but next time I have contact with Barry I will mention the update.
Not sure if its still ongoing but interested in 2.
Added. No idea either 
Please add me for another one. Hope this becomes a reality. 
Update: Barry has contacted me about the source of the LEDs.
I agreed to share the information, only for the purpose of making flashlights and we agreed that such information is confidential.
Looks like this project now has a real chance of coming to life. 
In for 2 , 4!
Interested in complete lights, posting to keep track
There is some movement at Sofirn towards a new batch of C01’s with the high CRI 5mm leds that rngwn found. I have not heard any timeline though. If that batch happens I assume I have a good chance getting the hosts done too.
I am in for another 2 hosts, making it 4.
I was recently looking to get a new Fenix E01 to practice/attempt an LED swap for my aged and loved E01. Sadly found Fenix had discontinued it.
Was having trouble sourcing LEDs in quantities of less than 1000, found the high CRI Sofirn C01, got excited, then realised that had been a limited run.
Now a new hope they will start up a new run 
Four hosts unanodized - thanks!
How about quantities of 50?
You can still buy the E01. But it’s no fun removing the epoxy.
While awaiting the C01 hosts, another 5mm AAA light caught my eye for a possible host candidate.
SBFlashlight just put his Klarus lights on clearance and amongst the gems is the Mi02. It’s a great performer right up there with the Fenix E01. I’m probably going to pick one up and see about swapping the angry-blue Nichia GS with a Hi-CRI Yuji, while I await the next batch of C01’s.
edit - sold out of Mi02’s now.
Interested in one.
interested in 2
interested in 3