Perhaps I'm just showing off my ignorance, but, here goes... My understanding is that the difference in compatibility between different cassette / rear derailer / right shifter sets -- for example Shimano 9 speed, 10 speed road, 10 speed MTB, 11 speed road, etc. -- is the amount of distance between shift points. By shift points, I refer to both cog-to-cog cassette spacing and gear-to-gear cable travel. The former is only related to the latter by designed ratio, one of SRAMs marketing gimmicks IIRC.

Now, it seems to me that it should be mechanically simple to adjust the amount that the end of the rear derailer cable travels for a given pull on a brifter lever. I assume that this is not common simply as a planned obsolescence profit generator. Sheldon Brown mentioned the alternative cable attachment method that alters ratio slightly for one particular mismatch. So, my question is, what else is available in this regard?

Are there small maker brifters that can be adjusted to a variety of pull/release travel distances? Are there intermediate -- within the cable run between shifter and derailer -- mechanical devices that are available? Or, are there reasonable easy to construct mechanisms for the bike hacker with limited metalworking equipment?

Sorry if this is a repeat, but most of what I read on the subject relates to specific pairs of components, i.e. ErgoPower 10 + Dura-Ace 10 or whatever. I'm trying to get at whether there is a more generally applicable solution that will allow one to upgrade components over a period of time without having to buy a whole groupset at once.