I'd always imagined Munch's Exoddus would be the game to follow Stranger. I don't see that the engine has anything to do with it: ME might not include shooting, but then surely OWI just don't include any protocols to initiate a shooting mode in that game.
Whatever, I'm not expert. I wouldn't want to abandon the Quintology for long, although I fully expect to the Stranger in future games.
As for submitting your work to OWI, there is no way they can take aboard your ideas without you being properly employed by them. Indeed, I know of several cases where they have said they simply cannot view certain fan art or media due to legal reasons. Some money-grubber even took the Inhabitants to court for incorporating his idea of giving the Mudokons more emotion and character in AE*, and since then OWI have compeltely understandably been wary about fans submitting work.
But having seen everything Shell Man has scanned in from the Polygon magazine, I'm convinced Oddworld have certainly not wandered from their path. Certain characters I still regard as not having as much merit as I might previously expected Oddworld to come up with, but really, I'm not worried about it anymore.
* That story has doubtlessly developed over time and from person to person, so don't take it as written.