Such a wealth of knowledge!
So I looked at a few, and from what I can tell the MTH tach board have an MSRP of about $7. It's fascinating that they sold "just" the tiny sensor chip for $5. I wonder how many of those they sold.
I also saw some LocoSound tach boards which apparently have a resistor added. Do you have any "Service Bulletin" type info given to Authorized MTH Techs that explains the need for this resistor? Hard to imagine why they would have a different design for the Locosound sensor vs. PS2/3??
Also, as for an OSHPark version that supports the QRE1113, I'd be amazed if MTH or whatever MTH becomes would have interest in frying such a small fish...they surely have bigger fish to fry. That is, if I understand it, the only difference between some of the tach boards is the spacer distance. Hence a raw PCB for anyone to order from OSHPark for $2 (shipping included) would be (IMO) a contribution to the hobby.
And while:
Nothing is so easy as the job you imagine someone else doing!
Perhaps there's someone else on OGR who sees this DIY PCB design and wants a real "project" to experiment with. I mean this is what the OGR discussion forum is all about....right?!