Hi Aloys:
Having the vis-blockers does help with the frame rate, but the main reason we were originally investigating the paging and sliding doors mechanism was the memory usage problem. For those folks who cannot fit the entire age into memory, vis-blockers won't help.
I'm wondering whether people really need to be able to run freely between districts. [I agree they need to run in between subdistricts; in between districts, I'm not too sure.] If we seal the red and orange openings on your diagram - forcing people to use Prin Pahts to go between districts - then we'll no longer see the lag while paging; it will only happen during the linking black-out. We can also open up access between the central hub subdistrict and the surrounding white subdistricts to make it easier to navigate around the white district.
Regarding the view from the top of the Hub: currently, the upper linking point is at an altitude where only the shells in the white district are visible. The inter-district walls are high enough to block out the view of all the other districts. The paging system currently pages in all the white district shells when you link into the hub area.
In the version of the hub that you have (J'anim's hub), is the upper linking point at a higher altitude where you can see past the inter-district walls?