The use case I'm thinking of is for IoT or robotics, where you have devices you want to manage being deployed into remote networks that you don't have much control over. It's really helpful in this situation if devices make outbound connections only, so that network operators don't have to configure their firewalls to port forward or set up a VPN.
Edit: clearer language
CloudFlare Access allows this, using the cloudflared daemon, which acts as a reverse proxy. It essentially means the endpoint can be closed off to incoming connections from the internet, and you don't need to maintain various firewall whitelist (and hope they don't go out of sync)
Is something like this on the roadmap for Boundary?
As you can imagine we did quite a bit of research with our existing users/customers while working on the design of Boundary. One thing we heard almost universally was "please don't require us to install another agent on our boxes". So we decided to focus initially on transparent use cases that only require running additional nodes (Boundary controller/worker) without requiring additional software to be installed/secured/maintained on your end hosts.
> the endpoint can be closed off to incoming connections from the internet, and you don't need to maintain various firewall whitelist
If you think about this a bit differently, a Boundary worker is also acting as a reverse proxy gating access to your non-public network resources. You can definitely use Boundary right now to take resources you have on the public Internet, put them in a private-only subnet or security group, and then use a Boundary worker to gate access. It's simply a reverse proxy running on a different host rather than one running on the end host. You wouldn't _need_ to add a firewall to ensure that only Boundary workers can make incoming calls to the end hosts, it's simply defense in depth.
I did basically the same thing years ago for remote console devices deployed inside various customer networks where I had little or no control over the network. At that time, I used OpenVPN to automatically connect back to our "VPN servers" -- providing access to the device even if it was behind two or three layers of NAT (which, unfortunately, wasn't uncommon!).