As a sysadmin, this sounds great (a bit 'brown trousers' for me personally, but great). However, one of my clients is entirely 'in the cloud', so no need for your truck of kit - just provide as many VMs as we like somewhere on t'internet. Ideally you'd be able to do this in a 'little internet' which has a VPN to get into it, has it's own DNS servers, and maybe ways to 'bend' or alter requests to other cloudy services, such as Google or Amazon such that the app 'thinks' its talking to the real, live production service, but actually it's talking to a test account or some such. That means I can spin up my clients world in your environment and have it think it was on the internet, but actually not interact with anything real - and I don't need to change every account and password baked into the code and config so I don't do any damage to real data.
Secondly, just like the backups and drills that most companies don't bother to do, they won't bother to hire a service like this either. You'll probably be able to make a few top-dollar sales to some big shops who already have very good DR procedures, but the little place (or even medium place) probably won't bother.
One way I could imagine this working would be to gain some sort of certification. Say for example, the fiduciary regulations of Elbonia were changed to say that all app providers must have externally verified DR capability, then your business would fit right in and solve that need - and you'd probably get lots of work, and hopefully lots of repeat work too. Short of regulations though, whatever certification you could come up with on your own wouldn't be worth enough to have people want to pay to get it.