I've been using LW 7 years but was not aware of the ability of using letters like that. Perhaps I stumbled across it accidentally whilst doing something else & didn't think twice about it lol

With LW 5.2.2, the download window is now available 'all' the time no matter if you're looking at Library, P2P network window or uploads or friends or a browse (that's an improvement compared to LW 4). You can also resize the download window to suit your needs as you suggested about LW 4 above.

But still no ability to do as you were hoping with the typing of letters in any of the windows.

The beta has also re-introduced some filters at the side of search results. And also added a couple new filters. Size, length & bitrate filters. Though a bitrate filter was possible to use in LW 4, it didn't have a slider.

Ability to browse uploaders was re-introduced in the beta to bring it back in line with LW 4.

The Beta will also auto-delete some of known virus files once download is completed (hash of file matches known virus spam.)

Try the beta out & see what you think. No damage done if you don't like the beta & wish to downgrade back to 5.1 or even 4. The Beta seems to be stable. There is a beta 5.2.3 coming but I'm not sure when at this point. I am aware they will be reworking the Library to improve it but ... not sure any of that work will show as early as the beta 5.2.3