i always thought that UO would do well as a free to play MMO, although i can't quite think of that many perks for paying accounts, or worthwhile micro transactions. the only draw i can see is housing and storage.
would be interesting though in theory. maybe free accounts could be referred to as 'nomad' or 'gypsy' accounts, while the paying accounts could be considered 'citizen' or 'lordship' accounts.
nomad accounts:
5 characters per server
no housing privileges, cannot co-own, cannot friend a private house
can only rent one vendor total per shard
bank account maximum of 25 items; cannot issue or store checks in bank account (but can still cash checks permitting space)
700 skill cap
225 stat cap, no stat scroll privileges
cannot join thieves guild
cannot create official guilds, but can join guilds (no higher than ronin rank)
certain limits on microtransactions
certain server limits
account does not age/no vet rewards
citizen accounts (<$6 a month):
6 characters per server
720 skill cap
230 stat cap
housing privileges (up to 2 story custom property)
limited vet rewards
no 'nomad' restrictions
lordship account (current pricing):
7 characters per server
housing privileges (no restrictions)
increased bank account (150 items)
increased housing storage
increased stable storage
full vet rewards accural
paying players having the option of 'suspending' accounts, or converting to lesser accounts loosing privileges agreed upon.