If you think about Miracle Day as a standalone John Barrowman mini-series, that just happens to star Eve Myles too, like I do. You can appreciate that it can stand on it's own away from the rest of the Torchwood world. Me and my mom watched this together. She is somewhat of a sci-fi fan, and definitely not a British anything fan. She's a cold-blooded American who voted for Trump! So I knew the plot of this series would be interesting to her and enough American to get her to watch. Even though she has never seen an episode of Doctor Who or Torchwood before.
The bold ideas were great conversational pieces. I haven't seen the whole idea of immortality fleshed out quite like it was in the series. Most times, especially in sci-fi the idea of immortality comes with the idea of invincibility too. So it was cool to get to see people actually getting hurt, while not being able to die. Sort of like the reverse of a Zombie Apocalypse. After all these years, she still talks about it every once in awhile, and of course whenever she sees Barrowman.
So we both would definitely be up for a follow-up Miracle Day, but I would welcome any new Torchwood.