In the latest versions of 7.4, the scrobbling account option in Last.fm Audioscrobbler and the account in Last.fm Radio operate entirely independently of each other.  

In prior versions of 7.4 and 7.3, if you changed the Last.fm Audioscrobbler option to a particular Last.fm account, that would automatically change the account which was shown in Last.fm Radio.  

The result (for those households who have multiple Last.fm Accounts) is that, if you want to play Last.fm Radio (your own personal account) you need to check/set both the Last.fm Radio Account and Last.fm Audioscrobbler account. This involves quite a few more button presses in the webui and/or the playerui and in the Controller.  It's also very easy to forget.

It is possible to implement an option which would allow users to keep Last.fm Audioscrobbler and Last.fm Radio in sync?

The way I envisage it would work is than changing Last.fm Audioscrobbler would automatically change the account in Last.fm Radio if "keep Last.fm Audioscrobbler and Last.fm Radio accounts in sync" was enabled and vice versa.  

The only practical issue I can see with this (I'm sure there may be technical issues!) is if someone wanted to play a different account's Loved/Recommended/Personal channel but scrobble that to their own account. This could be resolved by making sync an option which you could switch off temporarily or not put on at all.  Subscribers can do this already.

I'm not sure how big a group of people would be affected by this option - my impression is that I'm one of the only regular posters who uses multiple account at Last.fm, but it would enhance ease of use in my view.