i am on the same boat, want a walk around lens, used to own the 28-135 IS, but can't afford the 24-105L.
and always hope either Tamron or Sigma will produce a 24-105/ 24-120 F4 for various mounts.
I am sure there is a market for this kind of lens, Nikon release their 24-120 F4 last year or so, but its heavier than the Canon, Sony and Pentax user can also benefit if either Tamron/Sigma make one. aim it ~$600USD street price