I guess you can take on more and more services once you stand firmly on the ground and have a well established reputation in one niche, that's the case when hosts start reselling domains and domainers - hosting, godaddy and namecheap cases, sometimes hosts go for dedicated service and colo services reselling, like ***********.com.
Well, the things that prevent every company from offering lots of services to their resellers are the numerous highly-trained staff.
I see one major problem with reselling dedicated servers, and that's the problem of support. If you buy this service with support from your host, how are your clients' tickets answered?