Hi Paul, there is an extension planned that would enable metabox for Archives and other archive types without UI. It is currently next in line and @cybr (plugin author) says the earliest version that might contain this feature is 3.1.
However, I honestly don’t think it is reasonable to throw specific dates around, because of 2 major setbacks:
1. Technical aspect, how to makes this work without JavaScript among others.
2. Niche request. This request caters needs of very few and TSF currently needs to focus on needs/requests of the many. There are other more requested features that might get priority.
Every feature adds to code base, needs maintenance and brings compatibility concerns (Old PHP, WordPress core, other plugins…). As TSF is still being made by 1 person (@cybr) everything new has to be considered very carefully, because the time is becoming more scarce.
Rushing features might bring up some bad spaghetti in the code, less testing and potentially catastrophic scenarios if there was some major bug to occur. As a linux person, I much more prefer current slower development cycle with time for testing and rock solid stability. Not that there are no new features — Focus was released recently and it is massive addition. It provides users with unique perspective on keywords (you can read more on blog) and this is something that caters to many, it is unique, adds tremendous value in terms of SEO and focuses on the most important aspect of SEO, content. That is, my opinion and you might disagree.
Yes, having a nice description for your archive brings tiny–tinsy SEO benefit, but honestly it is sooo negligible when you consider how much time is needed to implement it as a feature. At least from my own experience, most archive pages are not that great and I think Google knows that too. If you really think otherwise, they can utilize categories or tags for this need (both have SEO metaboxes and make more sense). Or hack away couple of filters.
So if you really need this feature now and other plugins have it, you should use them instead and don’t wait for TSF to implement it. It would be only logical. It is not that we are going to be happy to see you use different plugins, but it is what it is ?? I hope you understand, and I am sorry I can’t produce specific ETA for you.