I am wondering about how feasible it would be to combine Solar Jetman and Metroid into a single game. Metroid is too slow and repetitive for me by itself nowadays. But if it were an excursion from Solar Jetman, where you periodically land the ship in a Metroid-y world, explore a little, go kill a boss, then get back in the ship and fly to another world, I would enjoy it. It's essentially the same idea as Blaster Master, where the vehicular exploration component is almost an entirely separate game from the overhead shooting component, and you go back and forth between them.
I have not hacked Metroid myself, but I know it has been thoroughly hacked and is reasonably well understood. Solar Jetman is on Mapper 7, which I have no experience with... It seems like the approach would be to "host" Metroid in the Solar Jetman game. Sprites and backgrounds seem easy enough; the challenge would be to bring in the physics, animations and (ideally) the sounds and music from Metroid.
Can someone with experience frame the approximate difficulty of this? I am able to understand and write ASM, work with a debugger, swap memory pages, etc., although I don't have nearly the depth of familiarity with the NES hardware and functionality that some users here do. I guess I'm looking for either a "forget it, too hard" or "actually, it wouldn't be so hard..." kind of answer (and why).