What would it take for Microsoft to offer these images without any kind of expiry but as part of a paid-for testing package? I would rather pay (say) £100 and then be able to setup all my VMs once than have to jump through various hoops every 90 days. Saving me the large download of the VM images themselves is only of limited usefulness, since there will always be the additional steps of installing system updates / patches and then local environment configuration (things like adding IP addresses for local development machines to C:\Windows\System32\drivers\etc\hosts). 

The recurring cost (in terms of time) of the latter step is nontrivial and I for one would rather just pay to work around these issues, but given that Windows XP (the main sticking point) can't be officially licensed any more, your choices seem to be between this recurring process or software piracy. I understand the whole point behind offering these images is as a developer outreach program, so why not go that extra bit further and offer a paid, non-expiring option?