Why would a main server be required if users can fluently interact across Instances? (which, imo, is an area where lemmy has the most margin for improvements)

I don’t think a “main” instance is something we want. If one instance completely takes over the whole federation, we will have another reddit debacle in a few years.

While Decentralization is not a silver bullet against monopoly (just look at what gmail did to e-mails), centralization seems to always kill independence once platforms reach a critical mass

I think with the influx from reddit, which gathers a lot of technical users (which I think are also among the first users to migrate), I can see lemmy getting a lot more contributors in the coming days/weeks.

Among the features I’d love to see happen, some would also address your concerns about the lack of centralization :

• Community federation : this would make it possible to “fuse” communities from different instances. The admin of a community would be able to add other communities as “subcommunities” and all posts from subcommunities would show up in the “main community’s” feed. If the relationship is reciprocal, the two communities would “sync” with each other in some kind of way.
• “multicommunities” : users would be able to create and share lists of communities that span multiple instances
• Better community discovery across instances