[iloveponies]

Mandatory SSH keys mitigates the brute forcing risk, and turns it into a nuisance. My employer presently has this arrangement and has done so for a while. Bastions only get you in the door: different entrances for different environments, users keys are only propagated to the machines they need.

[jumby]

Roger that. I keep thinking of my customer support people as non-technical and for whom ssh keys, port forwarding & bastion hosts are way over their heads but your point is taken. There are other (cheaper!) ways to secure an internal network.