Yes, Nisei cannot sell FFG’s sets. But players can print those cards for their own use and I don’t think FFG would try chasing them individually. Also, in many jurisdictions, I think they would not succeed doing this anyway, especially when it is impossible to buy the cards printed by FFG.
So, for me, the solution should be exactly how it was during FFG-Netrunner time. Each player is responsible for having their decks ready to play. Big majority of Netrunner organized play happens in places where it is easy and not very expensive to print things in colour. There are multiple such places in my city (Eastern Europe, about 800,000 inhabitants) including one which is open from 7 am every day, so someone travelling for a tournament from a small village can simply turn up there in the morning and print their decks. Printing 100 nice colour proxies at that place costs about the same money as 100 medium quality card sleeves, so definitely not a prohibitive cost. You just need a bit of research and preparation, to provide your opponents with good gaming experience.
And this should IMO be the default NISEI policy. Each player needs a deck, cards should be FFG originals or look close enough to be easily recognizable from the other side of the table (i.e. colour prints, because art is what most people use to recognize cards). If a player expects they are going to have trouble sticking to this, they should contact the TO and look for a solution. If a TO expects multiple players in their area to have trouble sticking to this, they can introduce local policy (and communicate it clearly each time they organize a tournament).
BTW this is a good rule to follow generally. Global policies should lean to the stricter side, and people should be allowed to introduce local, more relaxed policies. This way someone who had no time to read local policies can simply stick to the global one and be sure they still comply with whatever was agreed in the place they go to.