Somebody was whining about PCB density.
I want to do a board with about 105 relays. I'd prefer 130 but that's not going to happen.
Here's a trial placement, just to see what might fit.We normally use the TPIC6595 shift register as our relay drivers. But it's big and I'd need 14 of them. So I think I'll add another Trion FPGA and have its pins drive a logic-level SOT23 mosfet under each relay. The T20 is only about $11, about half the cost of 14 of the TI things.
I do need to be sure that the relays won't interact magnetically.
The coils will generate heat too, brickwalled like that. I think we'll use 24 volt relays and run them at 16 volts quiescently, to cut the power dissipation about in half. We can bump the coil voltage up to 24 for a few milliseconds, whenever we change the pattern. 
My production people think they have ideas for placing 100+ relays efficiently.
I have about 10 square inches on the right for the rest of the stuff I'll need. And there's always the bottom of the board. sorta like the Austin-Healey overdrive solenoid.