Starting with v10.0 you can use [InfiniteLine](http://reference.wolfram.com/language/ref/InfiniteLine.html)

    RegionPlot[
     InfiniteLine[{x, x - 1} /. {{x -> 0}, {x -> 1}}], 
     PlotRange -> {0, 100}]

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/2uPr1.png