Imaginary cartridge format with 2k + 2k banking:

 

Current memory footprint of map kernel, for each level/group of levels: 4k (code + data)

 

Splitting code+data into 2k+2k ...

 

Table: number of levels/groups, amount of ROM required:

 

1 4k 4k

2 8k 6k

 

et cetera.

 

Clearly a winner, even if part of the data area held duplicated code, or if part of the code area were wasted, making data have to be split across more banks.

 

This also would open up to having variations of the kernel in different 2k banks. Specially, I'd love to split out the venetian blinds lines so that they occur on odd frames in the first line of a triplet and in even frames on the last line, giving a banding effect that would be less noticeable I think. More like the "bad video-radio link" effect from Star Wars, with 50% effective reduction in intensity on two out of every 3 lines, the centre line being more firm.