What are you needing to use listtransactions for?
The reason I didn't implement listtransactions is I want to make sure web programmers don't use it. It would be very easy to latch onto that for watching for received payments. There is no reliable way to do it that way and make sure nothing can slip through the cracks. Until we have solid example code using getreceivedbyaddress and getreceivedbylabel to point to and say "use this! use this! don't use listtransactions!", I don't think we should implement listtransactions.
When we do implement listtransactions, maybe one way to fight that is to make it all text. It should not break down the fields into e.g. comment, confirmations, credit, debit. It could be one pretty formatted string like "0/unconfirmed 0:0:0 date comment debit 4 credit 0" or something so it's hard for programmers to do the wrong thing and process it. It's only for viewing the status of your server. I guess that would be kinda annoying for web interfaces that would rather format it into html columns though.