Heuristics upon boot wait time?

I still think if this cannot be done in an easy way and one just NEEDS to wait an unspecified amount of time, to just try with some heuristic (record wait times on different boots, interpolate and get the new wait amount). After a couple of boots one would know approximately how much to wait until all the (needed) devices are brought up. All that is needed is a way to store and pass on subsequent boots the needed information (previous wait time for example) so one can make a better guess.