I think your premises are wrong and what you propose is a monumentally bad idea.
I have several software products that are constantly upgraded free of charge.
So features of the Xpro3 and XT4 might not make it down to the XT3 and certainly not the XT30 despite same sensor and cpu because they don't have the time or money for it. Do you buy a new camera to get the better AF algorithm, distance scales, multi exposure features, classic negative, bleach bypass. Or would you pay for Fuji to give those to the XT3/XT30 features?
And for the number of software packages that will give you free updates for life, there is 100000 that will give small updates and big fixes for free but charge for big updates, so your premise is wrong because what you use final cut pro, that is probably subsidized to hell by apple.