None of us have heard anything on iTunes Match since it was announced by Steve. Months of delay without any further announcements.
I think you're right, it will increase over time. But being such a huge music fan, I hate waiting. I really need to back my music up now, not in 2012. Part of my trade is as a musician and a lot of the songs are my own work, would be great to have them in the cloud system. I'm only 4000 songs over the limit too.
You don't have to wait for iTunes Match to be able to back up your unusually large library.