The issue is more complex than just having enough time for all the nodes since they are not synchronized. The issue is that when the receiver is occupied with receiving one payload it cannot receive another and unless you start introducing acks, any transmissions that start during the time the receiver is occupied is lost, even with a minimal overlap of microsecs, the 2nd packet will be incomplete and fail CRC checks.
Even with short payloads there is a possibility that multiple nodes could transmit at the same time and cause dropped packets, the more nodes the more likely it is to happen. However since the nodes do not all send at exactly n Seconds the devices do not stay synced and every so often one will “overtake” another, whilst “overtaking” one or the other will be blocked. The closer the intervals are to each other in length, the longer the cycle of rotation and the longer it takes for “overtaking” Think 2 lorries on a dual carriageway at almost but not exactly the same speed, it takes forever for the overtaking to complete, Then extend the trailers on those lorries significantly (longer payload) and the effect is it takes much much longer.
As a rule you need to keep both the device count and the payload length short to combat the un-synced transmissions or accept there will be outages (frequent and short if the emonTH’s range in intervals or less often but extended, if the intervals are almost the same).
The reason the transmissions in existing sketches are not synced is because the receiver is put to sleep to conserve battery power so it cannot listen for a trigger, but that isn’t a concern when not using batteries.
As it happens I have a similar project coming up and I had originally planned to just hardcode the sensor id’s into the sketch as the failure rate of these is pretty low (I do not use rj45, I use permanent conns) so the R&D time to make the code handle whatif’s wasn’t justified in my mind. Since then I have been toying with creating an emonhub 1w interfacer so I could use a RPi zero wifi, overkill on the hardware for the task, but the 1wire interfacer would be reusable, even on an emonbase.
I don’t think there is any option that isn’t going to require some modding or code writing, but if if there are enough users wanting something similar, then many hands make light work, however finding a fit all solution is never going to be straightforward.