As for "John's still pursuing the noble goal of trying to produce the whole publication on RISC OS - leading to problems with passing on the right materials to the printers, it's believed.".
This is an amazing statement and hard to believe - not that he wants to use RISC OS but that there are problems with passing the material to the printers. Producing Postscript output should not be a problem (if you want the sprites to be of reasonable printing quality convert them to e.g. JPEG, put them in an ArtWorks image and put that into the document to print). Furthermore creating PDF for those less versatile printing offices who can't handle Postscript is no problem at all - be it using Ghostscript, or by now RiScript.
GAG-News is being published since 1992 regularly every two months with Impression and since 1993 using Postscript output which is then passed to the printers (in the very first days I printed it and used a quality copy shop until circulation allowed me to use a more professional approach). True, GAG-News is perhaps simpler than Quercus since it is in black and white. But I did the odd colour work and it went the same way, that is using Postscript and this time with colour separation.
The only two issues I had to look into are
1. set the lpi/dpi, that is resolution and halftoning/screen to sensible values - for simpler work 600 dpi/150lpi is fine, for high quality try something around 2500 dpi/150 lpi but the printer will tell you.
2. The way RISC OS Postscript includes sprites and perhaps other bitmaps etc. into colour Postscript output is bad news for bigger images - they do it in a manner which is formally correct but such that even good raster image processors can run into problems. Here again the trick to convert it into a JPEG (even with 100% quality) and then put that into an ArtWorks image for inclusion in Publisher - that works like a treat; it might work with other bitmap formats as well but I never tired.
If Qercus 277 and 278 are finished perhaps John might want to produce both in one go and send them out in one go. That might save hime a bit money (e.g. in postage) and work (just one mail shot) and make the subscribers a bit happier (average of 2 issues in six months instead of just 1)