I'd like to bring up a few things.
I'm a mentor on shivas NN and I'd say we are doing a good job in general regarding new players. Most leaflings don't want to leave the chat at all because forming communities is extremely easy, as is finding friends. 80% of my friend list is made out of former sprouts I've mentored and who did not want to leave NN because it has become their most important social community and after they leave, they try to get crafting mentor asap to return.

Since they immediately went from sprout to mentor they barely have experience to mentor others and can't answer a lot of basic questions and haven't had much experience when it comes to content.

A general chat would be very good, but yes it has to be regulated somehow. I honestly think that starting with lvl 70 you should be able to sign up for one general chat. That way, sprouts can form ties in the novice chat while they are novices and keep those once they are out of the chat without a linkshell. The thing with NN is that there are always new people coming an, so it's always fresh.

Since there are no RMT bots at lvl 70 they can't sign up for that.

As for moderation they could introduce a "moderator" role with harsh requirements. 3k Comms or whatever, those are the people who would be able to kick and moderate the chat but reports against them for unjust kicking would be immediately forwarded to a GM. Or there could be a "request GM" button that notifies a GM. 5 reports for unjust kicking and they can't become moderator for a while.
It's not ideal, I know, there is always some sort of power imbalance when it comes to letting your own community moderate itself.

This chat would also have clear guidelines like no trade chat, no FC advertisements, etc.

This would at least somehow offer an alternative to linkshells who -imo- are pretty flawed and way too small and static and give People a chance to socialize.

I'd also be up for monthly elections of moderators since I know at least 10 people in the NN who are always online and do great work when things get out of hand.