How about being able to play (against people of similar ratings) randomly generated positions with just a few pawns & pieces? That could be good endgame practice?
Farmer's Chess

True. You can currently start a game from one of about a zillion prescribed opening positions, but as soon as you want to start out from something a little unorthodox, it's impossible. It shouldn't be to difficult to install a function allowing one to simply make one's own starting position and then play from there.

Wrong. A win is more likely because king and pawn endings are so tricky.

I've heard of this as a game to practice pawn endgames, but I've never heard it called Farmers Chess.

Sounds like a good idea to me, this is one of the better chess variants I've seen. Monster would be another good one to add.

True. You can currently start a game from one of about a zillion prescribed opening positions, but as soon as you want to start out from something a little unorthodox, it's impossible. It shouldn't be to difficult to install a function allowing one to simply make one's own starting position and then play from there.
Another site I play at has that, though I don't think you could do the "Farmer's Chess" variant. I have never used it, other than a test, but it allows you to play games set up from FEN. I imagine that would get some use here.

An option to play games from an FEN string (unrated to keep ratings based on real games maybe?) would definitely be cool.

I've heard it called the pawn game. I think Seriwan or Silman mention it as a good training tool in one of their books.

Wrong. A win is more likely because king and pawn endings are so tricky.
of course it will not be draw if players are weak, but when the players are solid for example 1800-1900 or more position will be blocked in at least 80%

I'd like to try it -- I'd bet a stronger player wouldn't let you block anything and surprise you with some pawn breakthroughs -- remember it's a tempo game as well so I'm also betting the stronger play could create a fatal zugzwang again and again.
I am a big fan of King & Pawn endings, but so few games end up in that form. To get more practice, I have plalyed against the computer many times with just king & pawns - I did not know it was formally known as Farmers chess :)
It is not as simple as it seems. Like typical king & pawn endings, it involves a lot of delicate & precise calcuations. Play a few games of farmers chess & you will realize you are using so many chess concepts like: Triangulation, corresponsing squares, key squares, losing a tempo to get opposition.
Most of the games will not end in a draw. When I play with computer on a low depth, I beat it most of the times. On a higher depth level the computer usually gets the better of me. In my experience, draws have been few.
Farmer's chess is a great way to build your skills in K & P endgames. I am totally for chess.com supporitng this variant.

I think the reason it isn't on chess.com is because, as is plainly seen, you don't start with any pieces. When you start with one of those zillion opening positions, it's still chess, you're just requesting to start with a certain opening. When you play chess960 you aren't playing regular chess anymore, but a popular variant that has it's own separate rating. When you play farmer's chess, it would not be regular chess, and couldn't be rated as such, yet at the same time, it would not be a mega-popular variant like 960 that deserves it's own rating system.

It may gain in popularity. Besides, the same ELO rating subroutine that controls chess and 960 would work with farmer's chess. It's a quick game, good for learning endgame strategy, and judging from the flurry of comments this thread has generated, might see a lot of action.
There could also be Chinese Chess (Hsiang Chi) and Japanese Chess (Shogi) variants offered here - they're both fun games with enormous popularity.
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There's a chess variant (sort of) called Farmer's chess. It's basically just chess with only the pawns and the king. It's quite fun - good endgame training. I've tried to get www.chess.com to make it possible to play such a game against others, but so far my suggestion has not yet gone into effect.
Perhaps if this forum topic gets some commentary, it'll accelerate their intentions to add it to this site :-) So, let me know what you all think!