You can stretch availability to 99.9999999 if you have the money and the team to support it. However, each jump can incur up to a 100x cost increase per the Google SRE book. Availably is always a conversation about risk, innovation, cost, and what your customers will accept as an SLA.

Even Google doesn't go 99.999 on all services. Services that require rapid innovation are always lower because availability incurs an opportunity cost on innovation.