I think if Wargaming was to introduce a system where one clan member could lease his/her tanks to a clan mate for an up front cash rate and a percentage of XP and/or Credits earned by the Lessee during the lease period.
As an example:
One of my clan mates wants to lease a tank off me in a "try before you buy scenario", we enter into a deal where he pays 50,000 credits for a one week lease and I, as the tank owner, take 5% of his/her credits and XP earnings on the leased tank for that week.
I envisage the tank is leased on a "Lease and Run" set up, that is the tank is leased with 1 set of consumables, all the equipment and crew.
Wargaming could set the maximum lease tier, as an example, no person can lease a tank off another that is more that 2 tiers above the highest tier tank they have in their garage.
Wargaming could also stipulate a range on the initial lease payment and the percentage of earnings, and that too could be on a tier by tier basis.
I think this would be a great aspect of "Clanning" in World of Tanks and another great reason for people to join a clan.