I think an API call to a server is less demanding than visiting or scraping the site. So I don’t think a 3rd party app is going to cause more issues than the traffic itself, which the hosters already have figured out. Reddit issues with API calls aren’t that they cause increased server load, it was that they didn’t get to serve you ads or collect your data. Lemmy doesn’t do either of those so that isn’t an issue.

As of now, it’s all up to those who volunteered to host these open/large instances. They can accept donations but if they decide to shut down an instance, it’s gone. In the future I feel being able to gracefully handle instances disappearing would be the best bet. Financial reasons aren’t the only reason this could happen. Too many users could in theory break instances, as you can only scale vertically so much and at the moment I haven’t seen any talk of successful horizontal scaling. If users of an abandoned/deleted instance could easily move to another with minimal data loss this would mitigate this issue.

For long term viability, my opinion is legal entities (corporations, non-profits, etc) should be setup to handle larger instances that arise. They’ll operate as non-profits do, taking donations and hiring people to do the work that needs to be done. Expecting lone sysadmins to handle large user bases without some legal status/protection is a recipe for disaster. This also gives these larger instances a better standing to work within the current systems that will start asking questions/regulating if things get too big.

As for bringing in new users, these apps will have to make the process easier. It’s up to these apps to educate people or link to materials to educate people on the fediverse. These apps should be made to try and move users to instances that have the capacity to handle it and offer options. Yes, some users might find the fediverse and instances overwhelming but this is a common story with new things. Expecting everything to conform to how users currently operate is more for business interests, where user growth is a requirement for increased earnings and friction is bad.

The main concern with centralizing is once you have lemmy instances become centralized you arrive at the same position as reddit. What’s to say the largest lemmy instances won’t hold their instance hostage? Sell it to a corporation who liquidates it for the data and sees running the instance as a loss? Start defederating or limiting federation with other instances with malicious motives? If there is dozens of these larger instances, this will be easier to mitigate than the current handful of instances. It’s best if things are more decentralized, this is the goal of the fediverse after all.

Overall, lemmy isn’t ready for mass adoption as it stands. More work will need to be done and yes this is in “the future”. The current user base spiking doesn’t change the fact the code isn’t there, nor the fact code takes time. At the moment, you either suffocate instances by becoming too popular (lemmy.ml) or adapt and help contribute to get to the point where a large user base can be handled (such as mastodon has done).