I understand you need to prioritize features depending on the popularity of the platform or device your code is targeting. That's one of the reasons so many developers are writing iPhone apps.
But if you had to bet on a platform related to SQL Server, I think SQL Azure is a safe bet. Microsoft has invested over 2 billion dollars already on Azure and it's creating 5 data centers in the US that are over 500,000 square feet each. There's a similar data center being built in Dublin, Ireland as well.
Only the SQL Azure CTP is available and hundreds of thousands of invitation tokens have been sent. Check out the SQL Azure CTP forums and you'll see dozens of threads each day - and the CTP was released less than a week ago!
As mbaladi mentioned - SQL Azure works on port 1433 - it's TDS! That should minimize your efforts to make a version of SQL Compare that works with SQL Azure. Check out for example my two blog posts on scripts for SQL Azure:
Cleaning up scripts for SQL Azure
Windows PowerShell commands to clean up scripts for SQL Azure
I also opened a thread on the SQL Azure forums to share cleaning tips with other developers:
I spent 20 minutes and created the above PowerShell scripts that handle 90$% of my issues when cleaning up the generated scripts from SSMS for SQL Azure. I'm sure it wouldn't take you that long to come up with an integrated solution in SQL Compare.
Of course I can't make you fix SQL Compare so it works with SQL Azure - but even today you would make a lot of money from folks upgrading their old versions of SQL Compare to streamline their SQL Azure development. Seems line a no brainer to me.