This is going to be a short and sweet little history of Reddit. Reddit was founded in 2005.
Take a look at what Reddit looked like in 2006: https://web.archive.org/web/20061206235353/http://reddit.com/
Note that it didn’t have subreddits back then because the user base was too small.
Look at Reddit in 2008 (December 31): https://web.archive.org/web/20081231080128/http://www.reddit.com/reddits/
Politics had just 72,314 subscribers. Technology had 85,678 subscribers, and the “Nicher” Food subreddit had only 4,438 subscribers.
Lemmy/Kbin follows the same path. Initially, generalist communities like Politics and Technology will have the most momentum and gain subscribers, just like Reddit did back then. As the user base grows, “niche” communities will be able to sustain themselves.
Let’s not think about the Reddit of today, let’s think about Reddit of old. Rome wasn’t built in a day.
I agree, you want bums in seats as quickly and effortless as possible. Your average user coming from reddit just wants an “all” feed they can use to curate their own front page, they don’t really know, care, or want to learn about the plumbing underneath. The ones that do care will figure it out as theres plenty of resources available.
Knowing very little about the technical side - and speaking only from my experience trying to get my own account set up - I almost think the fediverse need a dedicated, standalone sign up instance (or series of instances) that has no posting enabled, but is automatically federated to the X most popular instances - so that apps and web interfaces can create simple default sign ups for new users without them needing to understand what instances even are.
Something like “lemmy.gateway” that can act as a home for the user account that then looks at the instances where the content actually happens, that can have high availability and redundancy in the event of server load on the popular instances, and that “just works” for your average reddit migrant so they don’t have to go diving into instance details to dip their toe in the water. That way your “content instances” can go up or down without impacting new user signups, your apps can work to load popular posts even if what would normally be your home instance is down, and you can decouple things a bit - maybe your “gateway” lemmy instance can drop some code to run leaner since it doesn’t have to worry about posting content.
To fund it you’d need some selfless souls, or perhaps agreement between major instances to shell out some revenue to host the sign up instance network, with the idea that getting users in to the fediverse generically is just as important as getting them on specific instances.
I have no idea if this is even possible but from a new user flow, if the intent is to maximise active users, you just want to get people “in” so they can eyeball, vote and post - then let learn how lemmy is different. Not the other way around.