Is this a viable format?

I was looking for something larger than 4x5. For some reasons I don't feel that 5x7 would make a large difference. 8x10 would be the next logical step. But for 6.5x8.5 I have at least a lens that covers it to start with. But the other formats do have film available. A lens is a one time cost, film comes always back. (ok, I know it rarely ends with a single lens) That would make 18x24 (metric) a better choice concerning film but not concerning choice of gear.