I just thought of this: When a clip with a filter is only in the Source tab, there is no actual way to deselect so that you don’t see any of the VUIs like you can do in the timeline. How about adding a deselect button in the Filters tab like here:
It would serve several purposes. It would allow a clip that is only in the Source tab to be played without any VUIs like I already mentioned. It would also be a visual cue for people who want to see the playback without any VUIs while working in the timeline to know that it can be deselected by pressing that button rather than clicking on another clip or even on the Output tab since the only way to actually see that option would be by right clicking away from any clips. Even then when people open that right click menu I think many miss the Select None option. And finally, it would serve as the more obvious way to drag a clip with Text: Rich from the Source tab to the timeline.
There is the issue that when deselecting is done in the timeline the whole Filters tab turns empty. Well, when it’s done with a clip in the Source tab then what could happen is that simply all of the buttons and values are still there but just grayed out. If you want to activate the Filter tab again with a clip in the Source tab then all you would have to do is just select one of the effects in the filters menu.