I think that works as a base. But I would remove some sites (up for discussion). I would remove following sites:

One thousand visitors or fewer
'Uruq Bani Ma'arid Saudi Arabia - not too hard. you just need the permit
Bassari Country Senegal - it's a bit far, but didn't see any reason to exclude it from a Senegal itinerary
Mount Hamiguitan Philippines - for those with a bit more relaxed interpretation of what counts as a visit, it was not too hard to visit

Most Remote Cultural WHS
All these places are within reasonable time accessible, if you don't shy away from driving. But other than the driving hours there are no opstacles.
Dholavira: A Harappan City India
Khinalig Azerbaijan
Paquimé Mexico
Rudreshwara (Ramappa) Temple India
Twyfelfontein Namibia

Not open to tourists
For these places it is commonly accepted within the community, that you see it from right outside the core zone and/or visit a replica.
Decorated cave of Pont d'Arc France
Genbaku Dome Japan
Stoclet House Belgium
Sundarbans National Park India
Thracian tomb of Kazanlak Bulgaria
Vézère Valley France

Red Zone Travel Advisory
We can at least remove serial sites, that can be visited in other countries. Not sure about sites in Lebanon and Iraq

We would also need to deduct sites, that are 2x or more on these connection lists.

Just to add to some considerations by winterkjim, Colvin and Rodinia, I am also among the "juniors", as it were, but were quite surprised when the app signalled me that I have visited 20% of the sites. With an enormous preponderance of cultural & European ones, but still 1 out of 5,it does not sound bad! And actually, I noticed that I managed to stay stable around this percentage and even increase it during the last WH sessions. This is to say, I'd say that with even with moderate dedication and means 500-600 are for sure at hand at the very minimum. But I fear that from that on the effort is less and less reasonable, or, in other words: there might not be too many obstacles to reach 1000, but it would still be a notable, directed effort. I am not sure if this is what you meant in the original post, though...

It's slightly out of topic, but for comparison, when I had some friends tick their sites, I noticed an average around 75. This makes me think about what is a "reasonable effort" :-D