It would be nice if vault exposed a set of economy api methods that allow plugins to include a description for each transaction. An economy plugin can use this to provide a useful transaction history for a player's account.

Vault is intended to provide API that already exists across the majority of economy plugins. As far as I'm aware there is no account history information in any of the major economies used, nor anyway to set information when a withdraw or deposit occurs.

I personally have written an economy plugin that supports it, and didn't bother publishing the plugin because its not compatible with vault. If vault provided the API, other plugins would use it, but without the possibility in vault, there's no point in an economy plugin adding the feature.

That's not how API additions to vault happen. Economies need to provide features, then Vault will sometimes pick them up and add them in. In addition, it's not Vault's responsibility to support every economy plugin, if an economy author wants to allow Vault enabled plugins to be used with their economy you simply register an Economy into the Bukkit service manager. It is not necessary for your economy to be directly linked in Vault.

Vault already provides API that economies don't use, so suggesting that API additions to Vault cause economies to add feature support beyond basic withdraw/deposit seems a bit unrealistic, and optimistically hopeful beyond what has already been proven over Vault's life. I'm also fairly confident that the feature wouldn't be something used except in extreme circumstances.

Totally understandable, but the reason I brought up the issue is because the idea can never work without direct support from Vault. Any plugin that wants to allow basic buy/sell functionality links to vault and uses that Economy interface in order to be compatible with a wide variety of economy plugins.

I've already done as you suggested, I provide the Economy interface, but I still need to link directly to my own Economy plugin in order to provide transaction descriptions, its fine for my own suite of plugins, but it's literally impossible for the economy plugin, or even the concept of transaction logging to gain any traction without support from vault.