As much as I would love an new 060 accelerator for the A1200 - the practical costs of it makes it VERY unlikely - not only in development costs, but also in sourcing compatible components for manufacture.
I think simple things would sell well and be of much benefit to the community - Now, lets talk *cheap* so lets talk Plastics =D
An idea that might be good could be - Custom A1200 Plastic casings and keyboards.
There are many companies that can manufacture plastics based on a prime-design, so imagine if you will multi coloured / opaque A1200 chassis with a housing designed for an SFF or Buffered IDE place for it to be screwed down, even and extention to the original chassis so that it could have a SFF CDROM drive underneath the FDD drive.
Theres quite a lot of possibilites with this as I am sure black/CBM White and Opaqe would be really BIG sellers.
Black Keyboard replacements would be a huge want with the customizers, theres a few companies I was in contact with when developing some custom chassis and they are quite low cost with low MOQ's too.