The clip border of the underlying clip could be a dotted line.
That dotted line could be reached by a TAB.
Like one can Tab to crossfade start and end already.
So, with a Tab to the underlying clip start and a Shift-Tab to the end of the overlaying clip, that selection could be used for a crossfade.
Maybe as a preference : Tab to clip boundaries, Sync Points, Fade borders AND underlying clip boundaries.
(Yes, I know about bring-to-front/back.)