Is the classic Jinshanling to Simatai hike is still closed?

I know Simatai has been opened for the public. But I've got no updates that its connection to Jinshanling is also opened. Sorry I cann't help you with that. BTW, if you want to visit SMT, you'd better book a ticket on its official web in advance, for only combo ticket is available on the spot.

Simitai is open but only if you enter via the fake water town. Essentially it was shut down for several years so they could build a fake water town with hotels etc, string lights along the east Simitai wall and generally make it tacky. To enter the wall you have to purchase a ticket to the water town. Officially they say anyone can go to the wall without the water town, but as you have to book ahead, if you are 1 or 2 travellers, you won't be getting to the wall only (it will be closed for that day). If you are a tour group then you have more chance. The current trend for the Jinshanling/Simitai trek is to walk up to tower 22 and exit to the east car park. Or walk down to around tower 4 I think it is and then turn around and return.
I would suggest to anyone, don't go to the water town. They set up a fake tourist site and now charge a fortune to visit what was originally a beautiful part of the wall-its now just a tourist trap.