Seems the OP misunderstood the context of VOR-DME in /I ops. As other posters have noted, it stands for RNAV based on VOR/DME boxes like the KNS-80. The other functions are relegated to INS or GPS/INS boxes that don't fulfill the /G criteria.
The thread title probably meant to ask if /A was a practical application in today's airspace. To which the answer is yes imo, but it does becomes limited and laborious over longer distances or in SID/STAR ops.
As to /I proper, in the case of military aircraft, they're highly prevalent among tactical aircraft mainly because the GPS functionalities contained in said aircraft have not been certified to the full extent of /G criteria due to monetary/cultural (fighter) decisions. Which is to say, for us in the mil world, we effectively behave like /G aircraft in the radar enroute environment, we simply cannot legally do certain things certified /G airplanes can. It's not much of a hindrance; it;s a sort of "/I in name only", aside from RNAV/GPS approach capabilities which are self-evident.
As to GA /I piston aircraft? I haven't seen a post-LORAN one other than those with KNS-80 boxes. They are an outlier way of being able to file direct legally whilst essentially navigating with the use of a handheld or VFR-mounted GPS. In order to genuinely fly /I using a KNS-80 would require a clusterfog of radial-dme points on a filed flight plan that would give even the most pedantic controller a headache. So yes, doing that [old school KNS-80 RNAV] would be impractical in today's GPS-waypoint dominated NAS.
