Are you joking? This blog post is evidence that donations do work, but that doesn't mean you can just throw money around, you still need to allocate them effectively.
They are currently pulling in ~$166K a year, which can fund a team of developers anywhere else than the most expensive places. Since Babel is a open source and supposedly international project, there is no reason to pay the people working on it SF salaries.
They are doing the classic mistake of trying to optimize for getting more funding as well instead of focusing on minimizing costs, which tends to be much easier.
If they really care about being sustainable, they'll eventually realize this. But as put by sebmck both here and on Twitter, seems the group as no interest in actually making sure Babel survives but rather want to extract as much money as they can before it's too late.
- Just doing things part time. I have a few projects like this. It's fun, it's apparently useful for others. I obviously limit time I spent on this. I don't financially benefit from this and I don't mind. Lots of stuff I use falls in this category. I make a living using that stuff; I don't mind returning the favor by putting in some time. IMHO this is the most undervalued part of OSS: people just doing the work because they can and because it needs doing.
- Consulting and charging better rates by virtue of being involved with something your customers care about and thus being well positioned to provide expert advice on that. Nothing wrong with that of course but it does remove development time from your project. But then eating your own dogfood can be instructive as well. Especially for development tools. Understanding your customers is a lot easier if you are working with them and they are paying you.
- Getting hired by a company to work on software. Linus Torvalds is the famous example here. Guido van Rossum is another one. This gets easier the more economically relevant your project becomes. Being involved in and associated with major OSS companies has brand value. Babel is relevant enough that there might be a company or two with some vested interest in using Babel.
- Providing perks to paying sponsors in the form of logos on a website, co-branding, conferences, meetups, access to support, etc. Lots of long lived OSS projects survive like this. Conferences are also financed like this. There is no shortage of VC funded companies that need to cozy up to developers that already spend millions on all sorts of stuff to do that. All you need to do is provide them a way to get recognized for that. It's also a great way to build the relationships that you might eventually level up to employment. Your community of professional users is a valuable resource that companies want access to that you can facilitate.