I don't understand why you need a special frame for these. Why can't you just drill some holes in the existing dropouts and bolt the new ones on?

This is a Tikit with standard vertical dropouts...where do you propose you drill some extra holes to bolt in the modular dropouts shown below?



Here is a side by side of a Season Tikit and a derailleur Tikit.



If you want modular dropouts you need to order them when you buy your Tikit...or I assume you could have them added after the fact by BF.

In those pics it looks like there's plenty of metal to drill holes of appropriate size and spacing. In fact, it seems you could bolt these dropouts onto the dropouts of almost any bike.

I think maybe BF doesn't endorse it because the width wouldn't be correct if the modular dropouts were bolted to the regular dropouts. In other words the special dropout holes seem to be offset laterally so the boltons are 135mm apart when bolted on. But surely there are plenty of ways to solve this like adding spacers if the boltons are too wide or just squeezing the hub in if the boltons are too narrow, right?

I sure don't see the adequate material to drill two additional bolts that would support a rear axle, but you are right the dropout width would be too narrow regardless.