I take the number ten in the article to be a recommendation, not a strict limit that will give you an error when you add the 11th user.
Query notification is not a very widely used feature, and I don't think it has been enhanced since SQL 2005 was released. So from that perspective, the limit would be the same. Then again, hardware today is much more better, and we only have 64-bit. Way back then, most SQL Server instances were 32-bit. So I would guess that you have quite a few more. Not the least if you count the total user base - not all may be waiting for query notifications at the same time.
But if it is critical for you - set up your own test.