Yes, you are right, for using this DB's at the max the shared hosting is not the place, but for projects starting small, with the chance to grow, the sharing hosting with this type of DB's is the right choice.
Me, for example, i don't know if the game will be a hit with many users, i don't even know if i will finish the game, and so i will not go for a VPS (i don't want be under pressure to finish fast ). I want to start small, if i will have many users i will move to a VPS, and then to a dedicated and the maybe multiple dedicated servers.
So maybe you can offer in the future some kind of service for hosting only this type of DB's (i mean without web hosting and other stuff, only the DB hosting). It may be also profitable for HawkHost, considering that nobody is offering hosting for this type of DB's, except MongoHQ. I don't know, is just a suggestion.
And i think that for now i will host the DB on MongoHQ, or on my home PC during the development, and soon I will get web hosting the hosting from hawkHost (in March is expiring the current hosting, but i will get sooner to have time to move my blog also here)