... I assume one could go foundationless in a long Lang.
Sorry if my questions are elementary. It has been a long time since I had bees.
Your questions are not elementary at all - to me. I began phasing over to all foundationless at the beginning of 2018. I can tell you this - foundationless mediums are a different breed from foundationless deep frames.
I haven't had much trouble with the foundationless mediums, even running them in the extractor (as long as they are attached on 4 sides). However, as I phased out my deep boxes (not quite done with this process yet) - I added foundationless frames to the deeps also.
Last week I split the queen and some brood out of a strong 2nd-yr hive with a deep brood box, into a Nuc. I was able to cut 5 frames for QC's in the remaining hive. About 2 hrs later, I walked by the Queens Nuc and saw honey pouring out of the front entrance, and all over the ground. Apparently the deep frame of stores I put in there collapsed. Lots of dead and dying bees. What a mess.
This is an example of how much less stable foundationless deep frames are.
... just something for your thoughts.