It would be nice if MM could route scrobbles through the Last.fm desktop application like this script used to do.

Any timeframe you have in mind for adding this feature?

It would also be cool to customize the plugin so that it reflects the ratings from MM, say >= 3 stars, automatically "love" the track in last.fm, but also have the option to "love" a track manually without it having any star ratings in MM (or star ratings < 3).

No, it doesn't support it and yes, it is planned.

Does the latest last.fm scrobbler plugin not support the "loved track" feature? If so, any plans to add it?

thanks