Are you buying new? Consider asking Moots how much more it would cost to make the same bike with a horizontal dropout, ie like the common Campagnolo dropouts of the '70s. They could cut the dropout out of 1/4" ti plate. That leaves both options open. (My custom fix gear has a modified ti horizontal dropout - super long, opens at the front and down, not forward and has slope midway between a conventional dropout and track end true horizontal. I have the drawing of it so if you want Moots to pursue this, PM me. My dropout is pure fix gear, no derailleur hanger, but adding that would be a simple addition to the shape to cut.)

My Peter Mooney was made late '70s when vertical dropouts were becoming popular. I asked for the older horizontal dropouts just so I could go to fix gear should I ever want to. 40 years later, I tried it so I could ride that year's Cycle Oregon fixd AND ride all the promised gravel on wide tires. The ride got canceled - fires, but fix gear on that bike, yeah! It has a new life.

This isn't an either/or. It can be a both/and. Moots has never done it before but there is no reason they couldn't and it would be a much more fun project for them than just another bike. THis would cost money, but a Moots is a keeper. You could be riding this bike a long time. Why outgrow it just because your interests change.

Ben