Great suggestions, Ed and Dave! Especially since you mentioned exactly those FPGAs which I have also been pondering. 
The package is an important constraint for me. It needs to fit between the DIP pin rows, i.e. can't be wider than 13 mm. A BGA seems unavoidable, but 0.8 mm pitch (maybe 0.65 mm?) is the smallest that can be used with the design rules of the low-cost PCB houses.
iCE40HX is particularly attractive in that respect. Available in a 9*9 mm² 121-ball BGA, where the power capacitors could still fit beside the BGA on the top side. It also requires only two supply voltages at modest current, hence small linear regulators would do. The only FPGA where I would hope to get by with a PCB populated on the top side only. But maybe a bit small and slow; it would definitely be a step down from the original GODIL.
ECP5 is unfortunately the worst from a package perspective. The only package that would fit is a 0.5 mm pitch 285-ball BGA. I have looked at the (incomplete) layout for the TinyFPGA EX -- it uses 6 layers, vias-in-pad, and blind buried vias. The message I get is "don't try this at home". 
Max10 is available in a neat 10*10 mm² 169-ball BGA with 0.8 mm pitch. (In its smaller versions, up to the 10M16 with 549 kbit of block RAM.) Medium price and certainly better performance than the iCE40HX. But I have not seen these used much in amateur projects and can't quite place them performance-wise -- how do they compare e.g. to the Spartan-3?
Spartan-7 is what I had originally started to look at for my "new and improved 65F02". With three supply voltages, one of them drawing enough current to justify a switching regulator, and a 13*13 mm² package it definitely needs a PCB populated on both sides. But that's probably true for anything above the iCE40, so I might bite the bullet. Also, the fast XC7S25-2 which I had considered for the 65F02 is not cheap -- nearly 50 Euros incl. VAT. But smaller and slower versions start at 18 Euros or so.
So maybe the Spartan-7 (on a PCB populated on both sides) is it? It would kill two birds with one stone, being powerful enough for a 65F02-style accelerator -- although maybe a bit complex and expensive for a pure GODIL? I will play with component placement a bit to see whether I can fit everything, including the rows of 5V and GND jumper pads, onto the small PCB.
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