I would also be very interested in 1861 being included in 18xx rails - as it is my favorite 18xx game.

The effort of including 1861 would be limited since its core elements are equivalent to those of other games already implemented (privates (1830), minors and merging/converting (18EU), State railway (1856)).

The biggest difficulties would be to add additional logic for:
(a) Merging vs. converting minors
(b) Folding minors/majors into RSR (which is different if compared to 1856)

I would volunteer to be a beta tester for a 1861 implementation.