Probably a long shot but I know a bloke who's looking at becoming the Australian agent for a new broker, Finevo.
They look like launching around August. They've commissioned the authors of XTick to integrate their charting package with a well known and stable backend trading platform (the name of the company escapes my aging memory).
Finevo are also in discussions with StrategyBuilder to offer Metatrader support thus giving them a ready made base of traders.
I've asked the fellow I know to ask Finevo for feedback on [a] how long Finevo would support MT3 (and therefore the current API) [b] if they obtain a Client API for MT4 whether they'd be looking to give this away to current MT3 Client API users and [c] whether the XTick Trading Backend also has an API and the details of same if it exists.
Will keep posted on an answer early next week supposedly. As I said, a long shot but worth the price of a chat and an email.
Cheers
Martin