I have seen a technique where they line old pipes with newer plastic, like pumping an inner tube into an existing line; is that possible with the pipes in the house or would that cost too much of its diameter? Could they make a <1mm lining like that (which may need to be reapplied every once in a while), or some other kind of treatment to stop the lead from leaching?
I mean that would still cost a lot of money and time to implement in every house that still has lead pipes, but it's probably cheaper than replacing all the pipes.
I think most of those technologies are point to point linings. I also assume curves in the pipe cause 'issues'.
The other side of this is, if these houses have lead pipes and need a full water system gut (and probably the replacement of every device that touches the water); why stop there and just seal everything else back up. You're _going_ to find all of the horrific issues that existed but no one had seen in the light of day before. Or make all new issues. (For a good reference program on this, watch any of the highlighted construction / make it right shows made by "Mike Holmes" (OK, just the Canadian ones, in the US he's been in new build series only.))
When going that deep to fix the problem there's a substantial risk the whole thing is going to just have to be demoed and something new build to really fix the problem.
I mean that would still cost a lot of money and time to implement in every house that still has lead pipes, but it's probably cheaper than replacing all the pipes.