I think what you're saying is that it would be nice to have a feature similar to portamento but play all chromatic notes between the first note pressed and a second note pressed if the two notes were played legato (with no substantial "key off" time separating the two notes). The DX7 had this feature and FM-X has "compatibility" with the DX7 -- so some effort was done to support, in Montage/MODX, what the DX7 can do. Unfortunately, glissando wasn't something that was carried over. Beyond just FM-X, it would be nice to have this feature for both AWM2 and FM-X. FM-X to have more compatibility and AWM2 because sampled instruments such as you've listed (brass, guitar, etc) can benefit greatly from being able to easily play fast chromatic runs or smears that are not pre-sampled (have a specific ending note).

If this is what you mean, then I did first notice the lack of glissando in Montage in 2016 when I reviewed what was and was not supported by the DX7 sysex converter. Primarily this meant FM-X just didn't support this feature - not that the converter wasn't complete. Although I participated in several threads wishing for this to be added, I never took that suggestion to ideascale. I researched if there as an existing idea - didn't find one - and created one.