Malindraug
I probably could pay for someone else's subscription if there was a WG-sanctioned (as in use ryzom.com to credit it, not send the cash to their paypal)system in place for it. Person bribes me with materials or a pocket-healing service of pre-agreed conditions, I pay in 5-10-15-30 day cards.
Would allow people to subscribe with the current system, except you can go on guild chat and say "uh guys.. my sub dies in 3 days and my paycheck is 2 weeks behind (freelancer woes.. sigh)" and score 3x 5day cards. Naturally, anyone who bypasses the Ryzomcard (tm) and goes to cash for mats risks the sanctions any normal MMO would give out for it. LOTS Item Mall games allow the sale of mall items for in-game cash, of course balance goes out the window hence why I don't even MENTION selling items, not even cosmetic. Ours is a slightly different case to say the least =D
(Would be nice to get some official reply on these lines of thought in this thread)
/rant off
This is exactly what the PLEX system does in EVE Online.
You pay someone elses sub for 1 month, he gives you ISK ( ingame curreny )..