Indiana Jones the IP will always have a place in many peoples hearts. It is part of the culture and will always be, even subconsciously. Indiana Jones (the name and movies) is synonomous with ADVENTURE and the "Action Adventure" genre. Whenever something, mediawise, comes out that is part of that genre people always say "It's just like Indiana Jones!". Some quick examples off the top of my head I can think of are the Brendan Fraser Mummy movies, or the Uncharted video games. There's so many others.
My point is that even if the last two movies weren't regarded so highly, the IP is still part of the culture. And for the younger crowds that maybe didn't grow up with their parents showing them the movies, they still understand that Indiana Jones = ADVENTURE. This is the vibe that alone his name brings.
And for the very unkowing people of the IP: Whenever I go to Disneyland and go on the Indy ride there's so many people around me that don't know the movies, but they understand the vibe and the ride is fun and easily understood by the character and story. Just like with Splash Mountain, as an example, many people, including myself, never saw the movie or even knew it came from a movie, but I could understand the story and vibe it was portraying. Indiana Jones Adventure in Disneyland does that well, and I find it hard to beleive they won't be able to bring that here as well, even with a new story.
Sorry for the huge rant, but for the people saying the IP is irrelevant, IMO you're just plain wrong, and even if you're right, it doesn't matter because irrelevant or not, people will ALWAYS understand what Indiana Jones represents... and ADVENTURE will never be irrelevant!