FWIW product engineers usually get bonuses for patents, so there's the obvious incentive of $5k in your pocket.
There are plenty of Principal RSDEs and some become Managers of technical leaders of teams, which sometimes even include researchers.
But of course, the track is not as clear and common as for plain Researcher or SDE (in a product team).
PS: As far as I know, the patent bonus are there for all (though I can't comment on values).
Also, if you're on a patent, you get the cube (and the cash).
There are plenty of Principal RSDEs and some become Managers of technical leaders of teams, which sometimes even include researchers.
But of course, the track is not as clear and common as for plain Researcher or SDE (in a product team).
PS: As far as I know, the patent bonus are there for all (though I can't comment on values).