No, there was an official statement
http://www.shipsim.com/ShipSimForum/index.php/topic,1071.0.html
I'm afraid, in a nutshell. No. There isn't going to be an SDK. But don't despair. The post above explains what can/can't be done.
Have a look around features and suggestions- there are several threads about UNofficial 'vote your favourite' ports/ships etc. Whilst these do not have any official backing from Vstep, you can be sure that they look at them and if something looks like being popular and selling enough copies of an add on... you never know.
Stu