According to a leaked email from a Samsung employee, the company is looking at starting their Android Lollipop rollout as early as next month. So far there have only been a few very specific models that have gotten the update, so this wave of updates should be pretty widespread.
The email suggests that the Galaxy S 5 will be first on the list, with the Note 4 and Note Edge right behind it. The Galaxy S4 and Note 3 shouldn’t be far behind that. No info on what other phones will be getting the update, but Samsung will supposedly begin working on their tablets after their current crop of phones is updated.
As a side note, this email mentions that Samsung is planning on updating its demo devices in the Samsung Experience Shops you can find in Best Buy with a date of January 4th, so you might be able to check out the Lollipop update on a display device as early as next week.