Do the blocked star systems become unblocked?

When looking over the Galaxy Map, I've noticed at least 3 star systems that apparently seem to be blocked out for me. The location of each system is where my cursor is hovering.

You can click through the images below for the larger versions.

The Mass Relay pathing seems to take me through them successfully and without trouble. However, I can't actually stop in them.

Will these star systems ever become unblocked areas that I can explore, or are they just in place to act as galactic "stepping stones" for the Mass Relays, so to speak?

If they are simply blocked until I reach a certain point in the story, I'd appreciate the plot point put behind a spoiler tag, please. :)

I have taken this map of all the available star systems and added the three spots you pointed out with big red X's:

It looks like you can not traverse to them. Due to the short range of some Mass Relays, they may just be there as identified lore Mass Relays from DLCs or books. I couldn't tell you which ones.