I don't think either one can be characterized as a "sorely lacking" feature.
I don't think we need to debate the degree of necessity. Suffice to say, it's inclusion would be beneficial to some users, myself included.
If 'play from here onward' is important, then presumably finding 'here' is as well. Both are resolved by using a view that includes only files not (fully) played. Then you get exactly what you want by playing the season or with 'Play All'. The view could also be restricted to the season currently being watched, thereby eliminating the need to select a season. A companion view could include only the episodes watched, those excluded from the first view, or all of them (i.e., the same view being used now).
We can already find 'here' well enough, but we cannot easily start playing from a random location in a video playlist.
Your suggestions are appreciated, but none of them give me anywhere near "exactly what I want"
Once I have finished watching a season of a show, the view restricting inclusion to only un-watched becomes useless. In addition, the time it would take me to craft the required views, including learning the language to write the expressions will take longer than the amount of time I'm trying to save.
I think a 'play from here' choice would be very useful, in a few different situations. If JRiver agree, I'll see it one day. If they do not, I will live without it, like many things in life
In getting back to the original question/request, I wonder if a particle could span files, instead of just including part of one. If it could, you could create a particle that included the 2 tracks you want to 'pin' together. Sort of like a reverse que file. I still haven't played with particles yet.
I suppose the real trick would be that if either part of the particle is called by a play/smart list, it forces the inclusion of the entire particle. I assume the intention is to 'permanently' combine some tracks 'automatically', so they are always heard together, without specifying or creating special playlists just for these few instances.