This very well might be the next iteration in fact. There is no "good reason" aside from simplicity. One of the reasons against this is var can take validation. So, you can do the following.

  var Integer do |id|

this will only continue if it matches against an Integer (and it will also cast it for you). The argument list might get hella complicated if you allow munging like that.

I am considering allowing chaining though, so,

  path('blog').var do |id|

What would you think of that?