The best bet for this idea is a generic engine much like the Nes version. Because of the particular limits of the 2600 and its specific optimization no single engine will facilitate every game type but that doesn't mean most games can't be distilled into a few select game engine types.
-Scrolling, this alone greatly affects what kind of game you make and requires different engines to be optimal.
Single Screen=Space Invaders, Donkey Kong, Frogger, Pac-Man
Page Flip=Adventure, Jet Set Willy
Vertical Scroll= Frontline, Xevious (Relatively easy to do compared to horizontal scroll.)
Horizontal Scroll=Defender, Empire Strikes Back (Usually very resource heavy to produce a smooth scroll.)
-Genre priorities, each game has specific needs and methods.
Shooter= Projectiles galore ie heavy Ball and Missile usage with line skips + scanline stagger or odd to even scanline flicker. EG. Take your pick Action52 had a ton, this can range from bullet hell Shmups to short limited bursts of projectiles like in Zelda.
Frenzy= Sprites galore ie using the Ball and Missle bits to render more sprites than the default 2. EG. Lock N Chase, Robotron.
Melee=A lot of horizontal attacking which needs Player object extensions made from Ball and Missile bits ie Roundhouse kicks, sword swings, grappling hooks. EG. Cheetahmen.
Puzzle=Mostly just blocks or other rudimentary shapes so plenty of opportunity for optimization and or pursuit of art friendly rendering techniques normally too impractical for action games.
Platformer=Mostly about solid collision and gravity simulation. EG. Mario Bros.
Well that's all I got for this topic for now, I hope this helps anybody confused or intimidated on where to start such an undertaking. I like the idea and I hope it gets off the ground someday.