'Someday' in context means it hasn't happened yet. The quote literally says nobody has developed a workable idea for a tinker class yet. A precise time for 'someday' isn't needed to make the point, because it doesn't make any difference if they do it next week or in 20 years, it still means they don't have a tinker class ready to go now, and it would need to be ready long before this if it were to appear in the new xpac. It's pretty easy to understand.
The date on the comment shows that there was no workable tinker class yet only about a month ago. Again I ask you if you think it is realistic that they'll insert a new class that they've developed from scratch into the xpac during the last month of the development cycle? Does that really sound like the way Blizzard pre-plans things to you? Is there anything in the quote you're relying on that suggests that at all? Because that's the only way your argument could make sense.