Trim Mode: keep 2-clip view during playback

You mean to loop playback with both sides of the trim playing?

It doesn't do that by design. Once you into a dynamic trim, you make the trim wiht JKL and then playback the edit which is only a single screen. That was you are seeing the edit in context of the change, if you were seeing both sides of the trim play then you wouldn't be able to see the edit point you just trimmed. At least that's the way dynamic trimming is designed to work, unless I'm not understanding what you want to do. 

But you cannot get it to loop ... in Trim mode, dynamic ... you have to keep hitting L then J to rewind.

At least, I cannot get continuous loop in Trim. Whether with Loop 'active' or not. 

I can get playaround to work, but that is only one screen at a time.

Now, when you're in Trim mode and JKL play, then both sides of the trim play in the trimming monitor. If you hit the Space bar to preview that trim, you only get the single monitor as you're watching the edit with pre and post roll. Even though you can dynamically hit an I (In point) during the trim preview and move the edit point. Very Avid like in how Premiere is trying to do it even though it's not quite a fluid as Avid. 

Both sides of the Trim does play when dynamic trimming. Just doing that very thing right now.