Just as me, you might be disappointed by Adobe's decision to no longer support Lightroom (4/5/6) as standalone programs. As owner of several licenses of various versions of standalone Lightroom, I was looking for alternatives. After having tried several commercial products, I decided to run LR5 as long as I can.
While I am not sure about LR6, 4 and 5 should be OK for the farther future.
However, there is a problem! Over the course of time, electronic cameras (not to call them digital) tend to fail after a few years and require replacement. Someone lately told me that film photography is for the rich. I am not sure about that, for the amount one pays for a new digital camera, a lot of film can be bought! Anyway, that is not my topic for today.
Lightroom RAW support for newer cameras strongly depends on Adobe's updates. With older versions of Lightroom no longer supported, such version won't be able to handle RAW files of "replacement" cameras. Or do they?
It appears that Adobe does not want to totally disappoint former customers, i.e. licensees. For many years, Adobe provides a DNG converter for free. This converter is actually kept updated for the time being.
So, with the additional step of converting directories of RAW files into DNGs, newer cameras will be indirectly supported in older versions of Lightroom.
Fingers crossed that Adobe does not decide to scrap the DNG converter!
The only workable alternative I know of would be RawTherapee. While for certain effects, I actually prefer RawTherapee, this software does not really compare to the general capabilities of Lightroom.
In a way it is funny how dependent a RAW-shooter is on a particular piece of software and therefore from the policies of a particular supplier. And yes, I do know about PHASEONE's Capture One, however, this just adds another dependency from a supplier.