Incandescent bulbs should be replaced with LEDs right now. The instant-on feature of LEDs combined with the low-cost of incandescent bulbs make immediate replacement financially wise.
But replacing compact fluorescent bulbs before they have failed is a foolish waste of money. Especially if you consider that LED bulbs will continue to drop in price if you wait a year or two. The savings in energy will be neglible for the remaining life of a used CFL bulb
It isn't as clear cut when it comes to fluorescent shop lights and other long fixtures. I don't think we should be casually suggest that anyone should rewire old fluorescent fixtures to accommodate LED replacements, but if you know what you are doing then that's a legitimate option. Certainly, there is no point in replacing worn-out ballast at this point. A new LED fixture is an option for folks looking for a suitable replacement.
I have a cabinet full of CFLs that I bought as replacements for worn-out CFLs over the years , so I am locked into those bulbs for several more years yet. But the last of my incandescents -- I think I am down to four bulbs in spots where I needed instant light and which get so little use that I haven't changed a bulb in 10 years -- will be replaced with LEDs soon.
I noticed recently that discount stores such as Walmart and Target have severely curtailed sales of CFLs in favor of LEDs. So the transition is well under way.