How about a "Split Edges" feature when exporting OBJs?

Since OBJ files don't support creased edges, when the resulting mesh is subdivided in a subdiv modeler, all the edges will sharpen unless you tediously assign creasing.

"Split Edges" refers to the fact that in the obj file, edges that should remain 'sharp' are exported as 2 closely spaced together edges seperated by small joiner polys. This edge then will remain sharp even upon subdiv in a modeler.

Another option, is to support the Collada subdiv format, which allows for creasing, or the Silo SIA format, which also allows setting edges as creased. SIA is a really simple format, a lot of other 3D apps are getting importers for it, and I think SILO and MOI are a potential match made in heaven. Model your tank in MOI, give it battle damage in Silo using Displacement Painting. Maybe if you ask nevercenter nicely, they'll give you some docs. :)