I was always confused by that Doraemon ROM (assuming it as some sort of broken MMC3 derivative), it's good to know how it actually works. I do wonder if, by that logic, it would be possible to convert the three Doraemon levels into separate NROM files (assuming they're confined to 32k chunks of data). I feel like it could take more effort than it's worth, though it could be a funky way around multicart compatibility.
Regarding the CHR-RAM conversions discussed earlier, there are a number of bootleg Contra ports utilizing CHR-ROM, mainly for plug & plays. The only other two bootleg CHR-ROM ports that I've come across are for DuckTales and The Little Mermaid, as well as Inventor's advanced hacks of Rad Racer and 1943 (F-22) if those count. I've attached one of the better Contra conversions below.