It's very risky to both teams, if you loan a really promising player and the other team doesn't use him, then you've spoiled a player, the risk of cheating is very high too, but with some conditions might be very good indeed.
I've been thinking about an option to "Try to buy a player", even if the player is not in the transfer market, you can make an offer to buy, with some conditions to avoid cheating (let's say minimum 1,5 times his market value, and the player is placed in auction like a normal player for sale) and the posibility to buy players for BOT teams (and maybe to inactive users?), so, increasing the number of good players managed by active users we'll keep national teams stronger too!
Of course, active managers would be free to refuse that offer if they want to, or send a counteroffer.