Re: Downey's last?
Other people could certainly be armored heroes, even ones outfitted with Stark tech, and work fine. Rhodes is just such a person.
However, a successor Iron Man? That is much dicier. It is *possible*, certainly, but it would require more than just "access to Stark tech." It would require someone who is a true genius with the heroic spirit, someone who could truly follow in Tony Stark's footsteps. The only obvious candidate would be "Tony's theoretical future kid," which wouldn't be relevant barring a fairly major time skip.