Could we have extra buyable guild slots in the crown store? I'm talking like 2 max, you could price them whatever, I'll buy them. I'm not particularly articulate rn as I haven't had much food today yet, but I hope this is something you could add in the future.
The only issue I can see with this is that letting players join more trading guilds then further limits the total number of players who can have access to a public guild trader. There are only 197 or so guild traders, so a max of 98,500 players can join those guilds.
Right now, that doesn't concern me. Most trading guilds aren't at full capacity, and are frequently recruiting new active members as some current members go inactive. Many active traders are in more than one trading guild, and we're not bursting at the seams right now.
That being said, I would expect that ZOS would have to look at the data of membership in trading guilds vs the available guild traders before they implemented a change that would let active traders take more of the available spots at public guild traders.