Its now running on a dedicated server with 6 cores/12 threads and 32 gb ram. I hope this will be enough for the near future. Nevertheless, new users should still prefer to signup on other instances.
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You should be able to do that without problems. However the main bottleneck is the database, I think some people want to experiment with read replicas. However as developers we would rather focus on optimizations which will benefit everyone, not only the largest instances.