So, we want to make the PiDP-1 a very affordable kit to make. Because, the more affordable the more chance that it will find its way to young coders who want to try their hand at PDP-1 programming!

But we're battling feature creep, we'll just have to add two spacewar controllers. The idea is to make it them tiny, low-cost PCBs that will do the job on their own, but at the same time, can be the PCB inside a proper custom-made wooden spacewar control box. As the original ones were all quite visibly one-off jobs too, a proper spacewar controller must look - artisanal.

But for those who do not like to tinker, they can use the PCB as-is:

As we had 36 extra IOs for lights or switches, we did spend the whole day thinking of other exotica to add. For instance, the three PDP-1s that made it onto Arpanet had extra button boxes - the time-sharing operating system used them to hook up multiple Teletypes. 

But we decided against such things, they can all be done in software and the kit is already a package of 15 PCBs as it stands. And though PCBs are cheap, it does add up.