The source package for EFP build-depends on xa65, which originates from the Atari computer scene. In order to get other free NES games into Debian, we'd have to first get their build dependencies sorted out, which mostly means their respective cross-assemblers.
From "Intent to package (ITP)" in Debian wiki:
Before filing an ITPUntil May 2015, cc65 proper (the C compiler) was non-free, while its binutils (ca65 and ld65) was free. With the C compiler being non-free and xa65 existing, there wasn't enough interest in packaging the binutils. But roughly four years after the relicense, cc65 appears set to enter Debian. It's in Debian 10 "buster", which is currently testing and frozen.
Find out if the software already exists in Debian. The existing package could have a different name to what you might expect, so do your search carefully and exhaustively.
Please research how many similar software packages are there actually in Debian, in what shape they are, whether they have active upstream and downstream maintainers. Such knowledge might prepare you to defend your ITP in favor over existing alternatives.
If similar (mature) alternatives exist, before packaging consider contacting upstream asking why they write this software. Maybe they can be convinced to combine their efforts with upstreams of similar packages to avoid duplicating the efforts and guaranteeing longevity of the combined project.
We'd still need to make some case for packaging NESASM and ASM6 though if a developer of a free game made with one of those assemblers wants it packaged. In particular, we'd need to find which fork of each gets the most maintenance attention.