I feel your pain for legacy systems. Mine is just one shared hosting server for clients I've had for years - clients whose sites still require PHP 5.2 and break if it's upgraded.
Short of ditching them I haven't figured out what to do. I'd hate to be a shared hosting company where thousands of sites break when the server software is upgraded (not to mention Wordpress installs getting hacked every day...)
We had a non-neglible number or clients still running on PHP 4. =( It's a dilemma indeed, because upgrading all of the servers and software is bound to break a huge portion of the websites, many of which have been loyal clients for years. (But don't have the dev experience to fix things.) Not upgrading things leads to degrading service, and upgrading things leaves a lot of clients with broken websites.
Also: hacked WordPress sites. The bane of my existence. I must've dealt with several hundred of them in my time.
Short of ditching them I haven't figured out what to do. I'd hate to be a shared hosting company where thousands of sites break when the server software is upgraded (not to mention Wordpress installs getting hacked every day...)