One possible alternative to either individual upgrades or new account categories would be the introduction of Benefit Packs. Benefit Packs would not be considered to be the same as accounts, but in addition to them. They would be available to buy either at the same time as purchasing a paid account, or separately, but would only be available to account classes of either Early Adopter or Paid Account and higher.
As an example, consider an Image Benefit Pack. With the possible advent of the new image server, we can hypothetically suggest that Paid Accounts get 1Mb of image space, Permanent Accounts 2Mb of image space. For the price of, for example, $10 for a 12 month period, users could buy an Image Benefit Pack. This would give them double their number of user icons, and double their amount of image storage space. In this fashion, while Permanent Accounts would still be expected to pay for Benefits if they wished to have them, they would still be rewarded for their account status, either artificially (by also lowering the prices of Benefits for Permanent Accounts) or inherently (Paid Accounts would go from 10 user icons to 20, Permanent Accounts from 15 to 30).
While this does not begin to answer all questions concerning user icons, it is one possible alternative. It has its drawbacks, in that users will be forced to pay possibly larger amounts for services that they may not need in order to get the perks that they wish. Also, there are numerous things to be considered for implication, such as what happens in the event of a Paid Account expiring before a Benefit Pack, what happens if a Paid Account with a Benefit Pack is promoted to a Permanent Account, would multiple Benefit Packs of the same type be allowed (presumable allowing the user to go from 10 to 20 to 30 user icons), and what would be the rules governing their expiry?
Depending on further LiveJournal growth constraints or paid features to be implemented, other types of Benefit Packs could also be introduced. If quotas and limits of any kind are introduced on journals, I can see an immediate demand by at least a small minority to have those quotas raised to some reasonable limit. A Benefit Pack for this would enable those users who exceed quotas to continue without changing their journal habits, and in a small way support LiveJournal.