Revolver ammunition uses what's called "Rimmed" cases, where the bottom of the brass comes out a bit in at the, well, rim. This is what holds the ammo in place. Rimless ammo is used by Automatic weapons (Semi- and full-automatic.).
There are a few rare revolvers that use rimless ammo, but they require half-moon and full-moon clips (The correct usage of the term for once, YAY!), which hold three or six rounds respectively.
Even rarer is revolvers that can camber and use any 9mm/.38 caliber ammunition. ... ... OK, it's one revolver, no longer produced, called the Medusa Model 47 Revolver. They successfully tested and claimed that it'd work with 25 different types of ammunition, with 117 possible types that could be used (Some of which are museum pieces. Yes, ammo so rare it's in a museum!).
Caseless ammunition, being just a square block, doesn't have a rim of any kind, so wouldn't be held by a cylinder. Unless it's Cap and Ball, then the percussion cap fits on the nipple.
I'm very familiar with revolvers I owned a S&W model 10 for a long time and have played with several others (and am currently in the market for a new wheel-gun, if I ever make up my mind on what I want). It's true that rimmed ammo is still the favorite in revolvers and Russian weapons, but it's old tech ...and moon clips (are used for rimmed or otherwise) come in sizes for 5-10 (someone told me 12 once but I've never seen a modern revolver that has that kind of capacity), with partials for 2-4... They're very effective speed loaders that many favor over the clunky multi-step alternative loaders.
The Medusa was more of an improvement on extraction and it addressed a problem that didn't exist (I hear some companies are still using the tech for single calibers), and it went the way of revolvers chambered in .700 NE. There's really only one man who's made improvements on the platform in over a century (that worked correctly and addresses active issues) and he's no longer alive. I'm very reluctant to say that there won't be major improvements on the platform by 2070. I know right now there's a push to partially seal and redirect escaping gases from the cylinder, front and back, making them safer to fire and easier to use in the dark (not talking about silenced revolvers). Hopefully we'll see that in the next two years?! The limited ammo is already being addressed with eight smoking rounds of .357 (that's as far as it'll go unless you want a .22), equaling the 1911 Coonan, and being more accurate than a steel 1911 by almost a minute without $2k invested to accurize it. Still it's only half the capacity of the plastic guns, but they're an additional whole minute less accurate. Can ya tell I like revolvers? I had a 2nd gen Glock 17 in 9mm (and several others through the years) that I went through police academy with, but it just wasn't the same as my six-shooter.
Not all caseless cartridges are square... I mentioned before in another thread (and seemingly had an argument) about how there are several varieties/shapes of caseless. Besides, roundish makes for less malfunctions when feeding and KISS still applies in combat.
If caseless is the only major advancement in firearms by 2070 then they would have figured out how to make it work in all the popular platforms (they had a hundred years to get it right), though 20 years to make the change means there's still a lot of "classic" guns floating around in cased ammo (nearly 200 years worth) that people grew up with and might prefer...
